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A068481
Numbers k such that gcd(k!+1, 2^k+1) > 1.
5
5, 9, 21, 33, 65, 81, 89, 113, 173, 209, 221, 245, 261, 281, 285, 309, 341, 345, 369, 393, 473, 509, 525, 545, 561, 593, 645, 725, 749, 785, 789, 833, 861, 873, 933, 953, 965, 1001, 1065, 1101, 1113, 1173, 1185, 1265, 1289, 1329, 1341, 1401, 1409, 1469
OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from G. C. Greubel)
MAPLE
select(n->gcd(factorial(n)+1, 2^n+1)>1, [$1..1470]); # Muniru A Asiru, Oct 16 2018
MATHEMATICA
Select[Range[2500], GCD[#! + 1, 2^# + 1] > 1 &] (* G. C. Greubel, Oct 15 2018 *)
PROG
(PARI) isok(n) = gcd(n!+1, 2^n+1) > 1; \\ Michel Marcus, Oct 16 2018
(GAP) Filtered([1..1470], n->Gcd(Factorial(n)+1, 2^n+1)>1); # Muniru A Asiru, Oct 16 2018
CROSSREFS
Cf. A000051 (2^n+1), A038507 (n!+1).
Sequence in context: A273410 A273486 A146867 * A146827 A297360 A216414
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 10 2002
STATUS
approved