A186710 a(n) = gcd(k^n + 1, (k+1)^n + 1) for the smallest k at which the GCD exceeds 1.

5, 7, 17, 11, 5, 29, 17, 19, 25, 23, 17, 53, 145, 61, 353, 137, 5, 191, 41, 43, 5, 47, 97, 11, 265, 19, 337, 59, 25, 5953, 257, 67, 5, 29, 17, 223, 5, 157, 17, 83, 145, 173, 89, 19, 5, 283, 353, 29, 12625, 307, 17, 107, 5, 121, 1921, 229, 5, 709, 241, 367, 5, 817, 769, 521, 5, 269, 137, 139, 725, 853, 55969, 293, 745, 61, 17, 29, 265

Offset: 2

Author

Michel Lagneau, Feb 26 2011

Keywords

• nonn

Comments

For k=0, the GCD equals 1. Increasing k, the GCD first exceeds 1 at k = A118119(n), and that GCD is a(n).

Examples

			a(2) = 5 because 2^2 + 1 = 5 and 3^2+1 = 2*5;
a(3) = 7 because 5^3 + 1 = 2*3^2*7 and 6^3 + 1 = 7*31.
		

Crossrefs

Cf. A118119.

Programs

Maple

A186710 := proc(n) local k ,g; for k from 1 do g := igcd(k^n+1,(k+1)^n+1) ; if g>1 then return g ; end if; end do: end proc: # R. J. Mathar, Mar 07 2011