Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #7 Apr 16 2016 03:03:33
%S 1,2,3,4,6,8,12,20,24,40,57,60,100,114,120,156,200,220,228,258,300,
%T 312,440,456,516,600,660,780,1032,1100,1140,1320,1560,1640,1752,1860,
%U 2172,2200,2280,2580,2964,3300,3660,3720,3820,3900,4344,4632,4902,4920,5060
%N Numbers n such that n^2 divides 7^n-1.
%H G. C. Greubel, <a href="/A127107/b127107.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[10000], IntegerQ[(PowerMod[7, #, #^2 ]-1)/#^2 ]&]
%Y Cf. A127100, A127101, A127102, A127103, A123104, A127105, A127106, A127092. Cf. A067947 = numbers n such that n divides 7^n-1.
%K nonn
%O 1,2
%A _Alexander Adamchuk_, Jan 05 2007