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%I #16 Feb 22 2021 04:03:39
%S 2,3,4,6,7,11,12,14,15,16,20,22,23,27,31,34,35,36,38,39,42,43,47,52,
%T 56,58,59,60,63,66,67,70,71,72,75,78,79,83,84,86,87,88,90,92,94,95,96,
%U 102,103,104,106,107,108,110,111,112,114,115,119,123,128,131,135,138
%N Numbers k such that k^k - 1 is squarefree.
%C 3^3 - 1 = 26 = 2 * 13.
%C 4^4 - 1 = 255 = 3 * 5 * 17.
%C 6^6 - 1 = 46655 = 5 * 7 * 31 * 43.
%t Select[Range@43, SquareFreeQ[#^# - 1] &]
%o (PARI) isok(k) = issquarefree(k^k-1); \\ _Michel Marcus_, Feb 22 2021
%Y Cf. A005117, A048861, A184967.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Mar 19 2011
%E a(23)-a(64) from _Amiram Eldar_, Feb 22 2021
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