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%I #13 Nov 20 2013 09:21:36
%S 1,4,5,7,8,11,12,13,16,17,19,20,23,24,25,28,29,31,32,36,37,40,41,43,
%T 44,47,48,49,52,53,56,59,60,61,64,65,67,68,71,72,73,76,79,80,83,84,85,
%U 88,89,91,92,96,97,100,101,103,104,107,108,109,112,113,116
%N Numbers n such that 1^(n+1) + 2^(n+1) + ... + n^(n+1) == 0 (mod n).
%H Charles R Greathouse IV, <a href="/A228919/b228919.txt">Table of n, a(n) for n = 1..10000</a>
%t f[n_] := Mod[Sum[PowerMod[i, n + 1, n], {i, 1, n}], n]; Select[Range[1000], f[#] == 0 &]
%o (PARI) is(n)=my(m=n+1);sum(k=1,n,Mod(k,n)^m)==0 \\ _Charles R Greathouse IV_, Nov 20 2013
%Y Cf. A191677, A121706.
%K nonn
%O 1,2
%A _José María Grau Ribas_, Sep 08 2013