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 A254653 #6 Jun 13 2015 00:55:24 %S A254653 1,3,58,276,6325,30303,695638,3333000,76513801,366599643,8415822418, %T A254653 40322627676,925663952125,4435122444663,101814618911278, %U A254653 487823146285200,11198682416288401,53656110968927283,1231753251172812778,5901684383435715876,135481658946593117125 %N A254653 Indices of centered heptagonal numbers (A069099) which are also pentagonal numbers (A000326). %C A254653 Also positive integers y in the solutions to 3*x^2 - 7*y^2 - x + 7*y - 2 = 0, the corresponding values of x being A254652. %H A254653 Colin Barker, <a href="/A254653/b254653.txt">Table of n, a(n) for n = 1..980</a> %H A254653 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,110,-110,-1,1). %F A254653 a(n) = a(n-1)+110*a(n-2)-110*a(n-3)-a(n-4)+a(n-5). %F A254653 G.f.: x*(2*x^3+55*x^2-2*x-1) / ((x-1)*(x^4-110*x^2+1)). %e A254653 3 is in the sequence because the 3rd centered heptagonal number is 22, which is also the 4th pentagonal number. %o A254653 (PARI) Vec(x*(2*x^3+55*x^2-2*x-1)/((x-1)*(x^4-110*x^2+1)) + O(x^100)) %Y A254653 Cf. A000326, A069099, A254652, A254654. %K A254653 nonn,easy %O A254653 1,2 %A A254653 _Colin Barker_, Feb 04 2015