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%I #10 Sep 08 2022 08:45:56
%S 1,4,1,2,1,4,2,2,1,1436,1,4,501969,4,1,644,1,5784852794328402307380,2,
%T 2,1,20,3,4,36,4,1,2,1,18353950678197027912484562396837972855962080,8,
%U 2,3,8,1,4,5,4,1,2,1,4,2,4,1,36,2,4,3,128,1,2,5,85840,2,4,1,12,1,16,273
%N a(n) is the least number k such that k*n+1 is a prime dividing n^n-1.
%C The smallest prime factor of n^n-1 of the form k*n+1 is A187023(n).
%e 7^7-1 = 2*3*29*4733; the smallest prime divisor of the form k*n+1 is 29 = 4*7+1, hence a(7)=4.
%t Table[p=First/@FactorInteger[n^n-1]; (Select[p, Mod[#1, n] == 1 &, 1][[1]] - 1)/n, {n, 2, 40}]
%o (Magma) A187025:=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; [ A187025(n): n in [2..50] ]; // _Klaus Brockhaus_, Mar 02 2011
%Y Cf. A187023, A187024.
%K nonn
%O 2,2
%A _Michel Lagneau_, Mar 02 2011
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