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 A328604 #34 Dec 13 2019 05:24:51 %S A328604 1,9,27,135,513,2241,9099,38367,158625,662553,2752731,11468439, %T A328604 47711457,198638865,826680843,3441111471,14322350529,59614704297, %U A328604 248130563355,1032793465383,4298762000961,17892665190369,74474188389387,309982363492095,1290232422488673,5370306116406201 %N A328604 G.f.: (1 + 7*x) / (1 - 2*x - 9*x^2). %H A328604 Colin Barker, <a href="/A328604/b328604.txt">Table of n, a(n) for n = 0..1000</a> %H A328604 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,9). %F A328604 a(n) = 2*a(n-1) + 9*a(n-2) for n>1. - _Colin Barker_, Oct 21 2019 %F A328604 a(n)/a(n-1) ~ 1 + sqrt(10). %o A328604 (PARI) Vec((1 + 7*x) / (1 - 2*x - 9*x^2) + O(x^30)) \\ _Colin Barker_, Dec 13 2019 %K A328604 nonn,easy %O A328604 0,2 %A A328604 _Kyle MacLean Smith_, Oct 20 2019 %E A328604 Edited by _N. J. A. Sloane_, Dec 05 2019