A067660 Values of gcd(k!+1,2^k+1) not equal to 1 taking k in increasing order.

2, 11, 19, 43, 67, 131, 163, 179, 227, 347, 419, 443, 491, 523, 563, 571, 619, 683, 691, 739, 787, 947, 1019, 1051, 1091, 1123, 1187, 1291, 1451, 1499, 1571, 1579, 1667, 1723, 1747, 1867, 1907, 1931, 2003, 2131, 2203, 6043, 2347, 2371, 2531, 2579, 2659

Offset: 1

Author

Benoit Cloitre, Feb 03 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A068481.

Programs

Mathematica

Table[GCD[n!+1,2^n+1],{n,0,4000}]/.(1->Nothing) (* Harvey P. Dale, Aug 03 2018 *)

PARI

for(k=0,3000,d=gcd(k!+1,2^k+1); if(d<>1,print1(d,",")))

Formula

If 2m+1 is prime and is in the sequence, 2m+1 = gcd(m!+1, 2^m+1).

Extensions

Corrected and extended by Rick L. Shepherd, May 20 2002

Offset corrected by Amiram Eldar, Jun 06 2022