This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A184966 #16 Feb 22 2021 04:03:39 %S A184966 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 A184966 56,58,59,60,63,66,67,70,71,72,75,78,79,83,84,86,87,88,90,92,94,95,96, %U A184966 102,103,104,106,107,108,110,111,112,114,115,119,123,128,131,135,138 %N A184966 Numbers k such that k^k - 1 is squarefree. %C A184966 3^3 - 1 = 26 = 2 * 13. %C A184966 4^4 - 1 = 255 = 3 * 5 * 17. %C A184966 6^6 - 1 = 46655 = 5 * 7 * 31 * 43. %t A184966 Select[Range@43, SquareFreeQ[#^# - 1] &] %o A184966 (PARI) isok(k) = issquarefree(k^k-1); \\ _Michel Marcus_, Feb 22 2021 %Y A184966 Cf. A005117, A048861, A184967. %K A184966 nonn %O A184966 1,1 %A A184966 _Vladimir Joseph Stephan Orlovsky_, Mar 19 2011 %E A184966 a(23)-a(64) from _Amiram Eldar_, Feb 22 2021