This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A068480 #15 Oct 16 2018 20:09:46 %S A068480 1,29,41,53,69,105,125,141,153,165,189,233,249,273,293,321,329,405, %T A068480 413,429,441,453,485,581,585,629,641,653,713,729,741,761,765,809,813, %U A068480 849,893,905,989,993,1005,1013,1041,1049,1089,1121,1125,1133,1169,1205 %N A068480 Numbers n such that gcd(n!-1,2^n+1)>1. %H A068480 G. C. Greubel, <a href="/A068480/b068480.txt">Table of n, a(n) for n = 1..1000</a> %p A068480 select(n->gcd(factorial(n)-1,2^n+1)>1,[$1..1230]); # _Muniru A Asiru_, Oct 16 2018 %t A068480 Select[Range[2500], GCD[#! - 1, 2^# + 1] > 1 &] (* _G. C. Greubel_, Oct 15 2018 *) %o A068480 (PARI) isok(n) = gcd(n!-1, 2^n+1) > 1; \\ _Michel Marcus_, Oct 16 2018 %o A068480 (GAP) Filtered([1..1230],n->Gcd(Factorial(n)-1,2^n+1)>1); # _Muniru A Asiru_, Oct 16 2018 %Y A068480 Cf. A000051 (2^n+1), A033312 (n!-1). %Y A068480 Cf. A068481, A068482, A068483. %K A068480 nonn %O A068480 1,2 %A A068480 _Benoit Cloitre_, Mar 10 2002