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 A188047 #17 May 04 2022 07:00:57 %S A188047 2,4,6,12,16,20,22,34,36,42,52,56,58,60,66,72,78,84,86,88,90,92,94,96, %T A188047 102,104,106,108,110,112,114,128,138,140,142,144,156,158 %N A188047 Numbers k such that k^k-1 and k^k+1 are squarefree. %C A188047 From _Kevin P. Thompson_, May 03 2022: (Start) %C A188047 a(39) >= 160 (160^160-1 is squarefree; 160^160+1 has no known square factors but is not completely factored). %C A188047 162, 186, 198, and 256 are also terms in this sequence. (End) %H A188047 <a href="http://factordb.com/index.php?id=1100000000009541993">Status of 160^160+1</a> %e A188047 6 is a term since 6^6-1 = 46655 = 5*7*31*43 and 6^6+1 = 46657 = 13*37*97 are both squarefree. %t A188047 Select[Range@42,SquareFreeQ[#^#-1]&&SquareFreeQ[#^#+1]&] %o A188047 (PARI) isok(k) = issquarefree(k^k-1) && issquarefree(k^k+1); \\ _Michel Marcus_, Feb 22 2021 %Y A188047 Intersection of A184966 and A184967. %Y A188047 Cf. A005117. %K A188047 nonn,hard,more %O A188047 1,1 %A A188047 _Vladimir Joseph Stephan Orlovsky_, Mar 19 2011 %E A188047 a(11)-a(25) from _D. S. McNeil_, Mar 22 2011 %E A188047 a(26)-a(31) from _Amiram Eldar_, Feb 22 2021 %E A188047 a(32)-a(38) (from FactorDB) added by _Kevin P. Thompson_, May 03 2022