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Numbers k such that k^2 divides 23^k-1.
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%I #10 Jun 11 2021 04:58:39

%S 1,2,4,6,8,11,12,20,22,24,40,42,44,60,66,78,84,88,120,132,156,168,212,

%T 220,264,312,420,424,440,444,462,474,546,620,636,660,780,820,840,858,

%U 888,924,948,1014,1060,1092,1218,1220,1240,1272,1320,1560,1640,1716

%N Numbers k such that k^2 divides 23^k-1.

%H Harvey P. Dale, <a href="/A128403/b128403.txt">Table of n, a(n) for n = 1..1000</a>

%t Join[{1},Select[Range[2000],PowerMod[23,#,#^2]==1&]] (* _Harvey P. Dale_, May 02 2015 *)

%Y Cf. A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128405, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128401, A128402, A128404.

%K nonn,less

%O 1,2

%A _Alexander Adamchuk_, Mar 01 2007