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A280003
Numbers k such that 7*2^k + 1 is a prime factor of a Fermat number 2^(2^m) + 1 for some m.
3
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
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
KEYWORD
nonn,hard,more
AUTHOR
STATUS
approved