A066507 Numbers k such that there is a solution to x^2 == 2^k (mod k).

1, 2, 4, 6, 7, 8, 10, 12, 14, 16, 17, 18, 20, 22, 23, 24, 26, 28, 30, 31, 32, 34, 36, 38, 40, 41, 42, 44, 46, 47, 48, 49, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 71, 72, 73, 74, 76, 78, 79, 80, 82, 84, 86, 88, 89, 90, 92, 94, 96, 97, 98, 100, 102, 103, 104, 106, 108, 110

Offset: 1

Author

Benoit Cloitre, Jan 04 2002

Keywords

• nonn

Comments

All even numbers are in this sequence.

Odd terms in the sequence are numbers whose prime factors are +-1 (mod 8) (A058529), i.e., odd k such that x^2 == 2 (mod k) has a solution. - Jason Earls, Jan 22 2002

Crossrefs

Cf. A058529, A001132, A057126.

Programs

PARI

isok(n) = {for (x=0, n-1, if (Mod(x, n)^2 == Mod(2, n)^n, return (1));); return (0);} \\ Michel Marcus, Nov 20 2013

Extensions

Corrected by Vladeta Jovovic, Jan 22 2002

More terms from Jason Earls, Jan 22 2002