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 A225115 #14 Mar 25 2018 08:29:39 %S A225115 3,15,120,528,4095,139128,160554240,812293020528, %T A225115 379188080252621270252095320 %N A225115 Triangular numbers of the form p^k - 1, where p is a prime number and k >= 2. %C A225115 There are at least other 4 terms greater than a(9) that can be easily obtained by solving the Diophantine equation T(n) = p^2-1, the smallest being T(75055187665070250755513356704300447). - _Giovanni Resta_, Apr 29 2013 %o A225115 (PARI) t=0;for(n=1,10^9,t+=n; if(isprimepower(t+1)>=2,print1(t,", "))); \\ _Joerg Arndt_, Apr 29 2013 %Y A225115 Cf. A006454, A025475. %K A225115 nonn,hard,more %O A225115 1,1 %A A225115 _Alex Ratushnyak_, Apr 29 2013 %E A225115 a(9) from _Giovanni Resta_, Apr 29 2013