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 A272361 #20 Jan 28 2019 13:58:06 %S A272361 182,546,910,1274,1638,2002,2366,2730,3094,3458,3822,4186,4550,4914, %T A272361 5278,5642,6006,6370,6734,7098,7462,7826,8190,8554,8918,9282,9646, %U A272361 10010,10374,10738,11102,11466,11830,12194,12558,12922,13286,13650,14014,14378,14742,15106,15470,15834 %N A272361 Numbers n such that (2^n + 1) / gcd(n, 2^n + 1) is not squarefree. %C A272361 Odd multiples of integer A002326((q-1)/2)/2, where q is a Wieferich prime A001220. %o A272361 (PARI) isok(n) = my(m=2^n+1); !issquarefree(m/gcd(n, m)); \\ _Michel Marcus_, Apr 27 2016 %Y A272361 Cf. A049096, A272359. %K A272361 nonn %O A272361 1,1 %A A272361 _Thomas Ordowski_, Apr 27 2016