A187024 a(n) is the least number k such that k*n+1 is a prime dividing n^n+1.

2, 2, 64, 104, 2, 16, 12, 8, 10, 2, 16, 1032, 2, 2, 17136, 2703399548648159360, 2, 5700, 7436, 16, 437174342164, 2, 1392, 9568, 2, 6, 16, 8, 2, 12, 20, 20, 176764, 2, 623673825204293256537467494040862720, 16, 5340, 2, 16, 440, 16, 22, 8, 990520

Offset: 2

Author

Michel Lagneau, Mar 02 2011

Keywords

• nonn

Comments

The smallest prime factor of n^n+1 of the form k*n+1 is A187022(n).

Examples

			12^12+1 = 89*193*233*2227777; the smallest prime divisor of the form k*n+1 is 193 = 16*12+1, hence a(12)=16.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 2..148

Crossrefs

Cf. A187022.

Programs

Magma

A187024:=function(n); for d in PrimeDivisors(n^n+1) do if d mod n eq 1 then return (d-1)/n; end if; end for; return 0; end function; [ A187024(n): n in [2..40] ]; // Klaus Brockhaus, Mar 02 2011

Mathematica

Table[p=First/@FactorInteger[n^n+1]; (Select[p, Mod[#1, n] == 1 &, 1][[1]]
  - 1)/n, {n, 2, 40}]