A Power Problem
Share:Problem. For how many prime numbers p, the expression 2p + p2 is a prime?
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Konstantin:
Only for p=3
30 December 2021, 12:15 amJBL:
On the other hand it seems that the expression is exactly 3 times a prime more than occasionally: 5, 7, 17, 43, 61, 73, … is not in the OEIS.
30 December 2021, 9:49 amCarl Feynman:
The expression should be a multiple of three half of the time, assuming a reasonable proposition: primes are equally distributed between multiples of three plus one, and multiples of three plus two. Consider the values of the expression modulo 3.
30 December 2021, 12:37 pm