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 A254675 #6 Jun 13 2015 00:55:24 %S A254675 1,13,44,776,2697,48069,167140,2979472,10359953,184679165,642149916, %T A254675 11447128728,39802934809,709537301941,2467139808212,43979865591584, %U A254675 152922865174305,2726042129376237,9478750500998668,168970632155735080,587529608196743081 %N A254675 Indices of centered triangular numbers (A005448) which are also heptagonal numbers (A000566). %C A254675 Also positive integers y in the solutions to 5*x^2 - 3*y^2 - 3*x + 3*y - 2 = 0, the corresponding values of x being A254674. %H A254675 Colin Barker, <a href="/A254675/b254675.txt">Table of n, a(n) for n = 1..1000</a> %H A254675 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,62,-62,-1,1). %F A254675 a(n) = a(n-1)+62*a(n-2)-62*a(n-3)-a(n-4)+a(n-5). %F A254675 G.f.: x*(12*x^3+31*x^2-12*x-1) / ((x-1)*(x^2-8*x+1)*(x^2+8*x+1)). %e A254675 13 is in the sequence because the 13th centered triangular number is 235, which is also the 10th heptagonal number. %o A254675 (PARI) Vec(x*(12*x^3+31*x^2-12*x-1)/((x-1)*(x^2-8*x+1)*(x^2+8*x+1)) + O(x^100)) %Y A254675 Cf. A000566, A005448, A254674, A254676. %K A254675 nonn,easy %O A254675 1,2 %A A254675 _Colin Barker_, Feb 05 2015