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%I #8 Jun 11 2021 08:49:02
%S 4,21,6,1555,8,889,10,111,12,253,14,2041,16,21,18,
%T 128583032925805678351,20,1432001198261,22,39,24,1081,26,55,28,171,30,
%U 279241,32,9641,34,1191,36,55,38,950123,40,1641,42,33661,44,32627169461820247,46,63,48,583223,50
%N Least number k > n such that k^2 divides n^k - 1.
%C For prime p, p divides a(p+1). Quotients a(p+1)/p for prime p = A000040(n) are listed in A128456(n) which coincides with A128357(n) for n from 2 to 6.
%C a(n) divides n^(n-1) - 1.
%F a(2n-1) = 2n.
%Y Cf. A128456, A128357, A128356, A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128401, A128402, A128403, A128404.
%K nonn
%O 3,1
%A _Alexander Adamchuk_, Mar 05 2007, Mar 09 2007
%E More terms from _Alexander Adamchuk_, Mar 09 2007
%E Terms a(22) onward from _Max Alekseyev_, May 05 2010
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