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 A258441 #11 Mar 07 2016 06:12:41 %S A258441 24486,959892121,37629690894906,1475159141502204841, %T A258441 57829188627539743273926,2267019851101653874322234161, %U A258441 88871712145057846553640480297546,3483948857243537849494160234302156081,136577763012789458630812222951472642381766 %N A258441 9-gonal numbers (A001106) that are the sum of two consecutive 9-gonal numbers. %H A258441 Colin Barker, <a href="/A258441/b258441.txt">Table of n, a(n) for n = 1..217</a> %H A258441 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (39203,-39203,1). %F A258441 a(n) = 39203*a(n-1) - 39203*a(n-2) + a(n-3). %F A258441 G.f.: -x*(x^2-32537*x+24486) / ((x-1)*(x^2-39202*x+1)). %F A258441 a(n) = (46+(89-36*sqrt(2))*(19601+13860*sqrt(2))^(-n)+(89+36*sqrt(2))*(19601+13860*sqrt(2))^n)/224. - _Colin Barker_, Mar 07 2016 %e A258441 24486 is in the sequence because A001106(84) = 24486 = 12036 + 12450 = A001106(59) + A001106(60), where A001106(k) is the k-th 9-gonal number. %o A258441 (PARI) Vec(-x*(x^2-32537*x+24486)/((x-1)*(x^2-39202*x+1)) + O(x^20)) %Y A258441 Cf. A001106, A258442, A258443, A258444. %K A258441 nonn,easy %O A258441 1,1 %A A258441 _Colin Barker_, May 30 2015