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 A319216 #33 Sep 17 2018 03:37:16 %S A319216 0,1,3,15,79,511,4095,6735,65535,2097151,16777215,75955411, %T A319216 68719476735,137438953471 %N A319216 Numbers k such that k^2 + 1 divides 2^k + 2. %C A319216 Numbers t such that 2^t-1 is a term are 0, 1, 2, 4, 9, 12, 16, 21, ... %C A319216 Primes p such that 2^((p^2-1)/2)-1 is a term are 3, 5, 7, 13, 19, 29, 37, 43, 47, 61, 71, 89, 103, 107, 127, 131, 139, 173, 191, 211, ...(cf. A062326). %C A319216 a(14) > 10^11. - _Hiroaki Yamanouchi_, Sep 14 2018 %o A319216 (PARI) isok(n)=Mod(2, n^2+1)^n==-2; %Y A319216 Cf. A015921, A062326, A097958, A244673, A247220. %K A319216 nonn,more %O A319216 1,3 %A A319216 _Altug Alkan_, Sep 13 2018, following a suggestion from _Max Alekseyev_ %E A319216 a(13) from _Hiroaki Yamanouchi_, Sep 14 2018 %E A319216 a(14) from _Giovanni Resta_, Sep 17 2018