A068480 Numbers n such that gcd(n!-1,2^n+1)>1.

1, 29, 41, 53, 69, 105, 125, 141, 153, 165, 189, 233, 249, 273, 293, 321, 329, 405, 413, 429, 441, 453, 485, 581, 585, 629, 641, 653, 713, 729, 741, 761, 765, 809, 813, 849, 893, 905, 989, 993, 1005, 1013, 1041, 1049, 1089, 1121, 1125, 1133, 1169, 1205

Offset: 1

Author

Benoit Cloitre, Mar 10 2002

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000051 (2^n+1), A033312 (n!-1).

Cf. A068481, A068482, A068483.

Programs

GAP

Filtered([1..1230],n->Gcd(Factorial(n)-1,2^n+1)>1); # Muniru A Asiru, Oct 16 2018

Maple

select(n->gcd(factorial(n)-1,2^n+1)>1,[$1..1230]); # Muniru A Asiru, Oct 16 2018

Mathematica

Select[Range[2500], GCD[#! - 1, 2^# + 1] > 1 &] (* G. C. Greubel, Oct 15 2018 *)

PARI

isok(n) = gcd(n!-1, 2^n+1) > 1; \\ Michel Marcus, Oct 16 2018