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 A254674 #7 Jun 13 2015 00:55:24 %S A254674 1,10,34,601,2089,37234,129466,2307889,8024785,143051866,497407186, %T A254674 8866907785,30831220729,549605230786,1911038277994,34066657400929, %U A254674 118453542014881,2111583153626794,7342208566644610,130884088867460281,455098477589950921 %N A254674 Indices of heptagonal numbers (A000566) which are also centered triangular numbers (A005448). %C A254674 Also positive integers x in the solutions to 5*x^2 - 3*y^2 - 3*x + 3*y - 2 = 0, the corresponding values of y being A254675. %H A254674 Colin Barker, <a href="/A254674/b254674.txt">Table of n, a(n) for n = 1..1000</a> %H A254674 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,62,-62,-1,1). %F A254674 a(n) = a(n-1)+62*a(n-2)-62*a(n-3)-a(n-4)+a(n-5). %F A254674 G.f.: -x*(x^4+9*x^3-38*x^2+9*x+1) / ((x-1)*(x^2-8*x+1)*(x^2+8*x+1)). %e A254674 10 is in the sequence because the 10th heptagonal number is 235, which is also the 13th centered triangular number. %o A254674 (PARI) Vec(-x*(x^4+9*x^3-38*x^2+9*x+1)/((x-1)*(x^2-8*x+1)*(x^2+8*x+1)) + O(x^100)) %Y A254674 Cf. A000566, A005448, A254675, A254676. %K A254674 nonn,easy %O A254674 1,2 %A A254674 _Colin Barker_, Feb 05 2015