A069226 a(n) = gcd(n, 2^n + 1).

2, 1, 1, 3, 1, 1, 1, 1, 1, 9, 5, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 27, 1, 1, 5, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 9, 1, 1, 1, 1, 25, 3, 1, 1, 1, 11, 1, 3, 1, 1, 1, 1, 1, 9, 1, 1, 1, 1, 17, 3, 5, 1, 1, 1, 1, 3, 1, 1, 13, 1, 1, 81, 1, 1, 1, 1, 1, 3, 1, 1, 5, 1, 1, 3, 1, 1, 1, 1, 1, 9, 1

Offset: 0

Author

Vladeta Jovovic, Apr 12 2002

Keywords

• nonn

Comments

First occurrence of n: a(1)=1, a(3)=3, a(10)=5, a(9)=9, a(55)=11, a(78)=13, a(68)=17, a(50)=25, a(27)=27, a(406)=29, a(165)=33, a(666)=37, a(301)=43, a(1378)=53, a(1711)=59, a(390)=65, a(81)=81, a(3403)=83, a(2328)=97, a(495)=99, ... - R. J. Mathar, Dec 14 2016

Links

• Antti Karttunen, Table of n, a(n) for n = 0..65537

Crossrefs

Cf. A006521 (fixed points), A014491, A049095, A049096, A060444.

Programs

Mathematica

Table[GCD[n,2^n+1],{n,100}] (* Harvey P. Dale, Dec 12 2012 *)

PARI

A069226(n) = gcd(n, 1+(1<Antti Karttunen, Jan 15 2025

Extensions

Term a(0) = 2 prepended by Antti Karttunen, Jan 15 2025