A280003 Numbers k such that 7*2^k + 1 is a prime factor of a Fermat number 2^(2^m) + 1 for some m.

14, 120, 290, 320, 95330, 2167800

Offset

1,1

Comments

18233956 belongs to this sequence, but its position is currently unknown. - Jeppe Stig Nielsen, Oct 05 2020

Links

Table of n, a(n) for n=1..6.

Proth Search Page, Prime factors of Fermat numbers

Eric Weisstein's World of Mathematics, Fermat Number

Prog

(Magma) IsInteger := func<k | k eq Floor(k)>; [n: n in [1..320] | IsPrime(k) and IsInteger(Log(2, Modorder(2, k))) where k is 7*2^n+1];

Crossrefs

Subsequence of A032353.

Cf. A000215, A050527, A057778, A201364, A204620, A226366, A280004.

Sequence in context: A221230 A240051 A202072 * A004312 A002056 A249980

Adjacent sequences: A280000 A280001 A280002 * A280004 A280005 A280006

Keyword

nonn,hard,more

Author

Arkadiusz Wesolowski, Feb 21 2017

Status

approved