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Numbers k such that k^2 divides 11^k - 1.
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%I #28 Jun 06 2021 09:01:31

%S 1,2,4,5,6,10,12,20,30,42,60,84,114,156,210,222,228,244,420,444,570,

%T 732,780,798,930,1092,1110,1140,1220,1554,1596,1806,1860,2220,2436,

%U 2964,3108,3612,3660,3990,4218,5124,5460,5772,6510,7770,7980,8268,8436,9030

%N Numbers k such that k^2 divides 11^k - 1.

%C Subsequence of A068383.

%H Seiichi Manyama, <a href="/A127092/b127092.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[15000], IntegerQ[(PowerMod[11, #, #^2 ]-1)/#^2 ]&]

%t Join[{1},Select[Range[9100],PowerMod[11,#,#^2]==1&]] (* _Harvey P. Dale_, Dec 30 2018 *)

%o (PARI) for(k=1, 1e4, if(Mod(11, k^2)^k==1, print1(k", "))) \\ _Seiichi Manyama_, Mar 25 2020

%Y Column k=11 of A333500.

%Y Cf. A068383, A127100, A127101, A127102, A127104, A127105, A127106, A127107, A292336.

%K nonn

%O 1,2

%A _Alexander Adamchuk_, Jan 05 2007