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 A254628 #11 Jun 13 2015 00:55:23 %S A254628 1,6,276,1891,88831,608856,28603266,196049701,9210162781,63127394826, %T A254628 2965643812176,20326825084231,954928097357851,6545174549727516, %U A254628 307483881705415806,2107525878187175881,99008854981046531641,678616787601720906126,31880543820015277772556 %N A254628 Triangular numbers (A000217) that are also centered pentagonal numbers (A005891). %C A254628 Also hexagonal numbers (A000384) that are also centered pentagonal numbers (A005891). - _Colin Barker_, Feb 11 2015 %H A254628 Colin Barker, <a href="/A254628/b254628.txt">Table of n, a(n) for n = 1..798</a> %H A254628 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,322,-322,-1,1). %F A254628 a(n) = a(n-1)+322*a(n-2)-322*a(n-3)-a(n-4)+a(n-5). %F A254628 G.f.: -x*(x^4+5*x^3-52*x^2+5*x+1) / ((x-1)*(x^2-18*x+1)*(x^2+18*x+1)). %e A254628 6 is in the sequence because it is the 3rd triangular number and the 2nd centered pentagonal number. %o A254628 (PARI) Vec(-x*(x^4+5*x^3-52*x^2+5*x+1)/((x-1)*(x^2-18*x+1)*(x^2+18*x+1)) + O(x^100)) %Y A254628 Cf. A000217, A005891, A254626, A254627. %Y A254628 Cf. A000384, A254962. %K A254628 nonn,easy %O A254628 1,2 %A A254628 _Colin Barker_, Feb 03 2015