Archive for the ‘Puzzle Hunts’ Category.

What’s in the Name?

  • 4, 6, X, 9, 10, 12, 14, 15, 16
  • 1, 2, 6, 24, 120, X, 5040, 40320, 362880
  • 2, X, 3, 4, 7
  • 1, 2, 3, 4, 5, 6, X, 8, 9, 153, 370, 371
  • X, 2, 3, 4, 5, 6, 7
  • 6, 28, 496, 8128, X, 8589869056, 137438691328
  • 0, 1, 1, X, 4, 7, 13, 24, 44, 81

This is the puzzle I designed for yesterday’s event at the Museum of Mathematics. This puzzle is without instructions — figuring out what needs to be done is part of the fun. Solvers are allowed to use the Internet and any available tools. The answer to this puzzle is a word.


2020 MIT Mystery Hunt

Every year I write about latest MIT Mystery Hunt puzzles that might be appealing to mathematicians. Before diving into mathy puzzles, I would like to mention two special ones:

Unfortunately math wasn’t prominent this year:

  • Food Court—This is a probability puzzle that is surprisingly uninspiring. There is no mystery: the puzzle page contains a list of probability problems of several famous types. But this puzzles can find great use in probability classes.
  • Torsion Twirl—Mixture of dancing and equations. I love it.
  • People Mover—Logical deduction at the first stage.

On the other hand, Nikoli-type puzzles were represented very well:

  • The Ferris of Them All—Several different Nikoli puzzles on a wheel.
  • Toddler Tilt—Not exactly a Nicoli puzzle, but some weird logic on a grid, some music too.
  • The Dollhouse Tour—Not exactly a Nicoli puzzle, but some weird logic on a grid, some pictures too.
  • The Nauseator—The first part of the puzzle is a huge nonogram.
  • Domino Maze—A non-trivial Thinkfun puzzle.
  • Backlot—Finding a path on a grid with a fractal structure.
  • Whale—Variation on Rush Hour.

Some computer sciency puzzles:


A couple of puzzles with the mathy side hidden:


Mathy Review of the 2019 MIT Mystery Hunt

Every year I review MIT mystery hunt from a mathematician’s point of view. I am way behind. The year is 2020, but I still didn’t post my review of 2019 hunt. Here we go.

Every year I review MIT mystery hunt from a mathematician’s point of view. I am way behind. The year is 2020, but I still didn’t post my review of 2019 hunt. Here we go.

Many puzzles in 2019 used two data sets. Here is the recipe for constructing such a puzzle. Pick two of your favorite topics: Star Trek and ice cream flavors. Remember that Deanna Troi loves chocolate sundae. Incorporate Deanna Troi into your puzzle to justify the use of two data sets.

On one hand, two data sets guarantee that the puzzle is new and fresh. On the other hand, often the connection between two topics was forced. Not to mention that puzzle solving dynamic is suboptimal. For example, you start working on a puzzle because you recognize Star Trek. But then you have to deal with ice cream which you hate. Nonetheless, you are already invested in the puzzle so you finish it, enjoying only one half of it.

Overall, it was a great hunt. But the reason I love the MIT mystery hunt is because there are a lot of advanced sciency puzzles that can only appear there. For example, there was a puzzle on Feynman diagrams, or on characters of representations. This year only one puzzle, Deeply Confused, felt like AHA, this is the MIT Mystery hunt.

Before discussing mathy puzzles I have to mention that my team laughed at Uncommon Bonds.

I will group the puzzles into categories, where the categories are obvious.

Mathy puzzles.

Here are some logic puzzles, in a sense that Sudoku is a logic puzzle.

  • Lantern festival—A cool mixture of Slitherlinks and Galaxies.
  • Invisible Walls.
  • Place Settings.
  • Middle School of Mines—Minesweeper.
  • Moral Ambiguity—Nonograms with a twist.
  • Connect Four—Mastermind. There was a strong hint that the extraction step was also mastermind. My team spent some time trying to mastermind the ending, until we backsolved. The extraction step was not mastermind. The final grid in the puzzle had the word CODE written in red. It corresponded to letters CDEO found at that location. Given that the letters were not in alphabetical order, it gave the ordering, which didn’t exist in the puzzle. Anyway, you can see that I have a grudge against this puzzle. This could have been a great puzzle. But it wasn’t.
  • Schematics—Tons of Nikoli puzzles of different types.

Now we have logic puzzles or another type, where you need to draw a grid. These are puzzles of the type: Who lives in the White House?

Now we have logic puzzles or yet another type, where you need to figure out which statements are true and which are false.

Now some cryptography.

And some programming.



Punny Puzzles at the MIT Mystery Hunt

This is a math blog, but from time to time, I write about other things. Today I have something to say about puns, which I adore.

I also like gym, but rarely go there: it doesn’t work out. I stopped using stairs, because they are up to something. I wanted to learn how to juggle, but I don’t have the balls to do it.

I work at MIT, the work place with the best dam mascot: Tim the Beaver. My salary is not big, and I stopped saving money after I lost interest. I’m no photographer, but I have pictured myself outside of MIT too. I am a mathematician, which is the most spiritual profession: I am very comfortable with higher powers. I praise myself on great ability to think outside the box: it is mostly due to my claustrophobia. I am also a bit of a philosopher: I can go on talking about infinity forever.

I would love to tell you a joke. I recently heard a good one about amnesia, but I forgot how it goes.

My biggest problem is with English. So what if I don’t know what apocalypse means? It’s not the end of the world!

I never get tired of puns and here is my list of pun puzzles from the MIT Mystery Hunt:


Mathy Puzzles at 2018 MIT Mystery Hunt

I was on the writing team for the 2018 MIT Mystery Hunt. I am pleased that the hunt got very positive reviews from the participants. I spent tons of hours working on the hunt and it is good that folks liked it. I edited and tested a lot of puzzles. Here is my review of these year’s puzzles that are math-related.

I already posted an essay about the puzzles I wrote myself. Four of my five puzzles are math-related, so I am including them below for completeness. I will mention the topic of each puzzle unless it is a spoiler.

I start with Nikoli-type puzzles. Four elegant Nikoli-type puzzles were written or cowritten by Denis Auroux. In all of them the rules of the logic are stated at the beginning. That means the logic part doesn’t contain a mystery and can be solved directly.

  • Good Fences Make Sad and Disgusted Neighbors (by Denis Auroux). You can guess by the title that this puzzle was in the emotions round corresponding to sadness and disgust. This is an interesting variation on the hexagonal Slitherlink. This is a relatively easy puzzle.
  • Shoal Patrol (by Denis Auroux and James Douberley). Each grid is a combination of Battleship, Minesweeper, and a loop puzzle. These are difficult, but satisfying puzzles. The extraction step is not mathematical and not completely trivial.
  • Submarine Patrol (by Denis Auroux and James Douberley). This is a 3D version of Shoal Patrol.
  • Hashiwokakuro (Count your bridges) (by Denis Auroux). This is a mixture of Hashi and Kakuro. I enjoyed the puzzle while I tested it. The extraction is trivial.
  • A Learning Path (by Tanya Khovanova and Xavid). This is a path logic puzzle that was targeted for new hunters. It contains self-referencing hints and solving techniques.

There were several puzzles that were very mathematical.

There were also some math-related or computer-sciency puzzles.

  • The Next Generation (by Colin Liotta). I enjoyed being an editor of this puzzle.
  • Disorientation (by Alex Churchill). This puzzle has a beautiful visual component.
  • Message in a Bottle (by Nathan Fung). The puzzle doesn’t look like it has something to do with mathematics, but my testing of it was very satisfying. I guessed from the start what it was about.
  • Self-Referential Mania (by Justin Melvin). Self-referential logic puzzle, which I enjoyed editing.
  • Bark Ode (by Elizabeth French, Justin Melvin, and Erica Newman). The pictures are so cute.
  • Executive Relationship Commandments (by Robin Deits, John Toomey, and Michele Pratusevich). I didn’t see this puzzle until after the hunt. I wish I could have tested this puzzle with my son Alexey, who is a computer scientist.

There were also several decryption puzzles:

  • Word Search (by Tanya Khovanova). A crypto word search.
  • Texts From Mom (by Elizabeth French and Justin Melvin ). A text enciphered with emojis.
  • Marked Deck (by Colin Liotta and Leland Aldridge). One of my favorite puzzles. Hunters received a physucal deck of cards that was laser cut. You can buy the deck at Etsy. The art in this puzzle is beautiful, but the puzzle also has a non-trivial decryption step.


My 2018 MIT Mystery Hunt Puzzles

I was on the writing team of this year’s hunt, which was based on the movie “Inside Out.” One of our goals was to create an easy first round to allow small teams to have a full hunt experience. Our first round consisted of 34 puzzles related to five basic emotions: joy, sadness, disgust, fear, and anger. Each emotion had its own meta puzzle. And the round had a meta-meta puzzle and a runaround. As I tend to write easy puzzles, I contributed three puzzles to this emotions round. The puzzles had references to corresponding emotions that were not needed for the solve path. They were inserted there for flavor.

I also wrote another easy puzzle called A Tribute: 2010-2017 (jointly with Justin Melvin, Wesley Graybill, and Robin Diets ). Though the puzzle is easy, it is useful in solving it to be familiar with the MIT mystery hunt. This is why the puzzle didn’t fit the first emotions round.

I also wrote a very difficult puzzle called Murder at the Asylum. This is a monstrosity about liars and truth-tellers.Share:Facebooktwitterredditpinterestlinkedinmail

Family Ties

The puzzle Family Ties was written for the 2013 MIT Mystery Hunt, but it never made it to the hunt. Here’s your chance to solve a puzzle no one has seen before. I wrote the puzzle jointly with Adam Hesterberg. The puzzle is below:

Mathematics professor S. Lee studies genealogy and is interested in the origins of life.

  1. Alexei Mikhailovich Ivanov
  2. Alexei Petrovich Ivanov
  3. Amminadab
  4. Anna of Moscow
  5. Arador
  6. Arahad II
  7. Arassuil
  8. Arathorn I
  9. Arathorn II
  10. Aravorn
  11. Argonui
  12. Asger Thomsen
  13. Caecilia Metella Dalmatica
  14. Egmont
  15. Eldarion
  16. Ellesar
  17. Endeavour
  18. Faustus Cornelius Sulla
  19. Henry Frederick
  20. Hezron
  21. Isaac
  22. Ivan the Great
  23. Ivan the Terrible
  24. Jacob
  25. James I and VI
  26. James V
  27. Jens Knudsen
  28. John Francis
  29. Joseph Patrick
  30. Joseph Patrick
  31. Jørgen Jensen
  32. Judah
  33. Knud Nielsen
  34. Margaret Stuart
  35. Maria Donata
  36. Mary Stuart
  37. Matthew Rauch
  38. Mikhail Ivanovich Ivanov
  39. Niels Møller
  40. Ole Pedersen
  41. Peder Petersen
  42. Peter Jørgensen
  43. Petr Alexeyevich Ivanov
  44. Pharez
  45. Ram
  46. Robert Francis
  47. Rose Elizabeth
  48. Søren Thomsen
  49. Thomas Olsen
  50. Ursula Gertrud
  51. Vasily I of Moscow
  52. Vasily II of Moscow
  53. Vasili III of Russia
  54. Yuri of Uglich
  55. Zerah


Mathy Problems from the 2014 MIT Mystery Hunt

The last MIT Mystery Hunt was well-organized. It went smoothly—unlike the hunt that my team designed the year before. Sigh. As I do every year, here is the list of 2014 puzzles related to math.

There were also several puzzles requiring decoding or having a CS flavor.

I want to mention one non-mathematical puzzle.

  • Operator Test. It is based on puzzles from the previous years and one of them was Wordplay, co-written by me.


Prepare for the Hunt

The MIT Mystery Hunt starts on Friday. My old team—Manic Sages— fell apart after last years’ hunt. My new team—Death and Mayhem—started sending us daily practice puzzle to prepare for the hunt.

Today’s puzzle was written by Paul Hlebowitsh. As usual, the answer is a word or a phrase.

Puzzle 3: Humans

“After a long day taking care of the animals, it’s good to unwind by letting the taps flow.”

Tap 1: Sierra Nevada Pale Ale
Tap 2: Lagunitas Pale Ale
Tap 3: 21st Amendment “Brew Free! or Die IPA”
Tap 4: Wachusett Blueberry
Tap 5: Harpoon UFO

Alice, Bob, Carol, Danny, Erica, Fred, and Gregario, the seven children of Noah, went to a local bar before the flood to get drinks. Accounts of night vary, and no one remembers exactly what happened, but some facts have become clear:

  1. Everyone had two drinks, in some order.
  2. Danny liked his first drink so much he had it again. Everyone else had drinks from different breweries.
  3. Erica was the only person to drink an IPA.
  4. Four people had the Wachusett Blueberry as their first drink.
  5. One person had the Sierra Nevada Pale Ale as their first drink.
  6. Alice only drank beers with headquarters in California, in order to spite Bob and Danny.
  7. Two Harpoon UFOs were ordered, as well as two Sierra Nevada Pale Ales. 8
  8. Alice’s second drink was the same as Fred’s first drink.
  9. Bob and Danny hate California and refuse to drink any beer from a company that’s headquartered there.
  10. Alice and Erica had the same first drink.
  11. Fred had a Harpoon UFO.

Who ordered which drinks and in what order?Share:Facebooktwitterredditpinterestlinkedinmail

Integers and Sequences Solution

This is the promised solution to the puzzle Integers and Sequences that I posted earlier. The puzzle is attached below.

Today I do not want to discuss the underlying math; I just want to discuss the puzzle structure. I’ll assume that you solved all the individual clues and got the following lists of numbers.

  • 12 42 18 40 30 24 20
  • 2 1 132 42 429 14
  • 7 9 1 8 5 3 10 4
  • 92 117 70 145 35 1 22 12 5
  • 137 1 37 13 107 1013 113
  • 30 12 2 42 6
  • 70 4030 836 7192

Since the title mentions sequences, it is a good idea to plug the numbers into the Online Encyclopedia of Integer Sequences. Here is what you will get:

  • not clear
  • Catalan numbers with 5 missing: 1, 1, 2, 5, 14, 42, 132, 429
  • not clear
  • Pentagonal numbers with 51 missing: 1, 5, 12, 22, 35, 51, 70, 92, 117, 145
  • Primeval numbers with 2 missing: 1, 2, 13, 37, 107, 113, 137, 1013
  • not clear
  • Weird numbers with 5830 missing: 70, 836, 4030, 5830, 7192

Your first “aha moment” happens when you notice that the sequences are in alphabetical order and each has exactly one number missing. The alphabetical order is a good sign that you are on the right track; it can also narrow down the possible names of the sequences that you haven’t yet identified. Alphabetical order means that you have to figure out the correct order for producing the answer.

Did you notice that some groups above are as long as nine integers and some are as short as four? In puzzles, there is nothing random, so the lengths of the groups should mean something. Your second “aha moment” will come when you realize that, together with the missing number, the number of the integers in each group is the same as the number of letters in the name of the sequence. This means you can get a letter by indexing the index of the missing number into the name of the sequence.

So each group of numbers provides a letter. Now we need to identify the remaining sequences and figure out in which order the groups will produce the word that is the answer.

Let’s go back and try to identify the remaining sequences. We already know the number of letters in the name of each sequence, as well as the range within the alphabet. The third sequence might represent a challenge as its numbers are small and there might be many sequences that fit the pattern, but let’s try. The results are below with the capitalized letter being the one that is needed for the answer.

  • abundAnt
  • caTalan
  • dEficient or iMperfect
  • pentaGonal
  • pRimeval
  • proNic or proMic
  • weiRd

What is going on? There are two sequences that fit the pattern of the third group and the sequence for the sixth group has many names, two of which fit the profile but produce different letters. Now we get to your third “aha moment”: you have already seen some of the sequence names before, because they are in the puzzle. This will allow you to disambiguate the names.

Now that we have all the letters, we need the order. Sequences are mentioned inside the puzzle. You were forced to notice that because you needed the names for disambiguation. Maybe there is something else there. On closer examination, all but one of the sequence names are mentioned. Moreover, with one exception the clues for one sequence mention exactly one other sequence. Once you connect the dots, you’ll have your last “aha moment:” the way the sequences are mentioned can provide the order. The first letter G will be from the pentagonal sequence, which was not mentioned. The clues for the pentagonal sequence mention the primeval sequence, which will give the second letter R, and so on.

The answer is GRANTER.

Many old-timers criticized the 2013 MIT Mystery Hunt. They are convinced that a puzzle shouldn’t have more than one “aha moment.” I like my “aha moments.”


  • (the largest integer n such that there exists a Platonic solid with n vertices, a Platonic solid with n edges, and a Platonic solid with n faces)
  • (the largest two-digit tetrahedral number)/(the smallest value the second smallest angle of a convex hexagon with all integer degrees can have)
  • (the number of positive integers less than 2013 that are divisible by 100, but not divisible by 70)
  • (the number of two-digit numbers that produce a square when summed up with their reverse) ⋅ (the smallest number of weighings on a balance scale that guarantees to find the only fake coin out of 100 identical coins, where the fake coin is lighter than other coins)
  • (the only two digit number n such that 2n ends with n) − (the second smallest, and conjectured to be the largest, triangular number such that its square is also triangular)
  • (the smallest non-trivial compositorial number that is also a factorial)
  • (the sum of the smallest three positive pronic numbers)


  • (the digit you get when you sum up the digits of 20132013 repeatedly until you get a single digit) − (the greatest common factor of the indices of the Fibonacci numbers divisible by 13)
  • (the largest common divisor of numbers of the form p2 − 1 for primes p greater than three) − (the largest sum of digits that can appear on a 12-hour digital clock starting from 1:00 up to 12:59)
  • (the largest Fibonacci number, such that it and all positive Fibonacci numbers less than it are deficient) + (the difference between the sum of all even numbers up to 100 and the sum of all odd numbers up to 100) − (the first digit of a four-digit square that has the first two digits the same and the last two digits the same)
  • (the smallest composite Jacobsthal number) ⋅ (the only digit needed to express the number of diagonals of a convex hendecagon)/(the smallest prime divisor of 132013 + 1)
  • (the smallest integer the fate of whose aliquot sequence is unknown) + (the largest amount of money in cents you can have in American coins without having change for 2 dollars) − (the repeated number in the aliquot cycle of 95) ⋅ (the second-smallest integer n such that the Russian word for n has n letters)
  • (the smallest positive even integer that’s not a totient)


  • (the number of letters in the last name of a famous Russian writer whose year of birth many Russians use to help them memorize the digits of e)
  • (the number of pluses you need to insert in a row of 20 fives so that the sum is 1000)
  • (the number of positive integers less than 2013 such that not all their digits are distinct) − (the number of four-digit numbers with only odd digits) − (the largest Fibonacci square)
  • (the number of positive integers n for which the sum of the n smallest positive integers evenly divides 18n)
  • (the number of trailing zeroes of 2013!) − (the number of sets in the game of Set such that every feature is different on all three cards) − (an average speed in miles per hour of a person who drives somewhere with a speed of 420 miles per hour, then drives back using the same route with a speed of 210 miles per hour)
  • (the smallest fortunate triangular number)
  • (the smallest weird number)/(the only prime one less than a cube)
  • (the third most probable product of the numbers showing when two standard six-sided dice are rolled)


  • (the largest integer number of dollars you can’t pay if you have an unlimited supply of 9-dollar bills and 13-dollar bills) − (the positive difference between the two prime numbers that do not share a unit digit with any other prime number)
  • (the largest three-digit primeval number) − (the largest number of distinct SET cards without a set)
  • (the number conjectured to be the second-largest number such that two to its power has no zeroes) − (the largest number whose cube has at most two distinct digits and no zeroes)
  • (the number of 5-digit palindromic integers in base 5) + (the only positive integer that is five times the sum of its digits)
  • (the only Fibonacci number that is a double of a prime) + (the only prime p such that p! has p digits) − (the only fixed point of look-and-say operation)
  • (the only number whose concatenation with itself is prime)
  • (the only positive integer that that differs by 1 from a square and a nonsquare cube) − (the largest number such that its divisors are each 1 less than a prime)
  • (the smallest admirable number)
  • (the smallest evil untouchable number)


  • (the alphanumeric value of MANIC SAGES) + (the sum of all three-digit numbers you can get by permuting digits 1, 2, and 3) + (the number of two-digit integers divisible by 9) − (the number of rectangles whose sides are composed of edges of squares of a chess board)
  • (the integer whose standard Roman numeral representation is alphabetically later than all others) − (the number you get if you divide a three digit number with identical digits by the sum of the digits)
  • (the largest even integer that is not a sum of two abundant numbers) − (the digit in the first position where e and π have the same digit)
  • (the number formed by the last two digits of the sum: 1! + 2! + 3! + 4! + . . . + 2013!)
  • (the only positive integer such that if you sum the digits and the squares of the digits, you get the original number back) + (the largest prime factor of the smallest Carmichael number)
  • (the smallest multi-digit hyperperfect number such that more than half of its digits are the same) − (the sum of digits that cannot be the last digits of squares) ⋅ (the largest base n in which 8n is not written like 80) ⋅ (the smallest positive integer that leaves a remainder of 2 when divided by 3, 4, and 5)
  • (the smallest three-digit brilliant number) − (the first decimal digit of the number that in hexadecimal gives the house number of Sherlock Holmes)


  • (the number of evil minutes in an hour)
  • (the number of fingers on ten hands) − (the smallest number such that its square has a digit repeated three times)
  • (the number of ways you can rearrange letters of MANIC)/(the number of ways you can rearrange letters of SAGES)
  • (the only multi-digit Catalan number with digits in strictly decreasing order)
  • (the smallest perfect number)


  • (the largest product of positive integers that sum up to 10) + (the smallest perimeter of a rectangle with integral sides of area 120) − (the day of the month of the second Thursday in a January that has exactly 4 Mondays and 4 Fridays)
  • (the second-largest number with all distinct digits, such that all the words in its American English representation start with the same letter) + (the largest square-free composite number that contains each of the digits 1, 2, 3, 4 exactly once in its prime factorization) + (the number of ways you can flip a coin 10 times so that the number of heads is the same as the number of tails) + (the smallest positive integer such that 2 to its power contains 2013 as a substring) + (the sum of five prime numbers formed from the digits 2, 3, 5, 7, 8, 9 where each digit is used exactly once) + (the number of days in a year where the day of the month is odious) + (the sum of the digits each of which spelled out has an alphanumeric value equal to the meaning of life, the universe, and everything) ⋅ (the sum of all prime numbers p such that p + 20 and p + 40 are also prime) + (the first digit of the total number of legal moves of the Black king in chess)
  • (the second-largest three-letter palindrome in Roman numerals)/((the smallest composite number not divisible by any of its digits)/(the last digit of 20132013) − (the digit in position 2013 of the string formed by concatenation of all integers into one stream: 123456789101112…)) − (the number of days in a year such that the month and the day of the month are simultaneously composite)
  • (the second-smallest cube with only prime digits) ⋅ (the smallest perimeter of a Pythagorean triangle)/(the last digit to appear in the units place of a Fibonacci number) + (the greatest common divisor of the sums in degrees of the interior angles of convex polygons with an even number of sides) + (the number of subsets that you can form from the set {1,2,3,4,5,6,7,8,9} that do not contain two consecutive numbers) − (the only common digit of 2013 base 8 and base 9)