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 A236967 #27 Sep 08 2022 08:46:06 %S A236967 1,12,72,324,1296,4860,17496,61236,209952,708588,2361960,7794468, %T A236967 25509168,82904796,267846264,860934420,2754990144,8781531084, %U A236967 27894275208,88331871492,278942752080,878669669052,2761533245592,8661172452084,27113235502176,84728860944300 %N A236967 Expansion of (1+3*x)^2/(1-3*x)^2. %H A236967 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-9) %F A236967 For n >= 1, a(n) = 4*n*3^n. - _Robert Israel_, May 08 2014 %o A236967 (Magma) m:=30; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1+3*x)^2/(1-3*x)^2)); %Y A236967 Cf. Expansion of (1 + k*x)^m/(1 - k*x)^m where the values of k,m are: %Y A236967 ......|..m = 1..|..m = 2..|..m = 3..|..m = 4..|..m = 5..|..m = 6..| %Y A236967 k = 1 | A040000 | A008574 | A005899 | A008412 | A008413 | A008414 | %Y A236967 k = 2 | A151821 | A241204 | | | | | %Y A236967 k = 3 | A099856 | A236967 | | | | | %Y A236967 k = 4 | A081654 | | | | | | %Y A236967 ------------------------------------------------------------------- %K A236967 nonn,easy %O A236967 0,2 %A A236967 _Ilya Lopatin_ and _Juri-Stepan Gerasimov_, Apr 22 2014 %E A236967 Edited by _Wolfdieter Lang_, May 07 2014