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%I #10 Sep 08 2013 02:28:33
%S 1,2,3,4,5,7,8,9,10,11,13,14,15,16,17,19,21,22,23,25,26,27,28,29,31,
%T 32,33,34,35,37,38,39,41,43,44,45,46,47,49,50,51,52,53,55,56,57,58,59,
%U 61,62,63,64,65,67,68,69,70,71,73,74,75,76,77,79,81,82,83
%N Numbers n such that 2 * (1^n + 2^n + 3^n + ... + n^n) == 0 (mod n).
%C See A228870 for the numbers not in this sequence.
%C Union of A226872 and the positive odd integers (A005408).
%C Also, positive integers n such that (p-1) does not divide n for every odd prime p dividing n (cf. A124240). - _Max Alekseyev_, Sep 07 2013
%H Vincenzo Librandi, <a href="/A228869/b228869.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[100], Mod[2*Sum[PowerMod[k, #, #], {k, #}], #] == 0 &]
%Y Cf. A228870, A226872.
%K nonn
%O 1,2
%A _T. D. Noe_, Sep 06 2013
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