A066787 a(n) = gcd(2^n + 1, n^2 + 1).

1, 5, 1, 17, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 65, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 41, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 29, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 565, 1, 1, 1

Offset: 1

Author

Benoit Cloitre, Jan 18 2002

Keywords

• nonn
• easy

Comments

a(n)=1 or a(n)=0 mod(5) or a(n) is a prime congruent to 1 mod(4).

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Programs

Magma

[GCD(2^n+1,n^2+1) : n in [1..100]]; // Wesley Ivan Hurt, Jan 03 2016

Maple

A066787:=n->gcd(2^n+1,n^2+1): seq(A066787(n), n=1..100); # Wesley Ivan Hurt, Jan 03 2016

Mathematica

Table[GCD[2^n + 1, n^2 + 1], {n, 100}] (* Wesley Ivan Hurt, Jan 03 2016 *)

PARI

a(n) = { gcd( 2^n + 1, n^2 + 1) } \\ Harry J. Smith, Mar 25 2010