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 A254230 #6 Jun 13 2015 00:55:23 %S A254230 1,4141,85285,429332905,8842505113,44514094237813,916808615026525, %T A254230 4615310318335580305,95056550814337645681,478524604381155542930941, %U A254230 9855653300615347164456661,49614388026831658683830230201,1021853845419343873890857865865 %N A254230 Heptagonal numbers (A000566) which are also centered square numbers (A001844). %H A254230 Colin Barker, <a href="/A254230/b254230.txt">Table of n, a(n) for n = 1..399</a> %H A254230 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,103682,-103682,-1,1). %F A254230 a(n) = a(n-1)+103682*a(n-2)-103682*a(n-3)-a(n-4)+a(n-5). %F A254230 G.f.: -x*(x^4+4140*x^3-22538*x^2+4140*x+1) / ((x-1)*(x^2-322*x+1)*(x^2+322*x+1)). %e A254230 4141 is in the sequence because it is the 41st heptagonal number and the 46th centered square number. %o A254230 (PARI) Vec(-x*(x^4+4140*x^3-22538*x^2+4140*x+1)/((x-1)*(x^2-322*x+1)*(x^2+322*x+1)) + O(x^100)) %Y A254230 Cf. A000566, A001844, A254228, A254229. %K A254230 nonn,easy %O A254230 1,2 %A A254230 _Colin Barker_, Jan 27 2015