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 A118979 #12 Jun 13 2015 00:52:06
%S A118979 12,72,300,1080,3612,11592,36300,111960,342012,1038312,3139500,
%T A118979 9467640,28501212,85700232,257493900,773268120,2321377212,6967277352,
%U A118979 20908123500,62736953400,188236026012,564758409672,1694375892300
%N A118979 O.g.f: -12*x^3/(-1+x)/(-1+2*x)/(-1+3*x) = -2-2/(-1+3*x)-6/(-1+x)+6/(-1+2*x) .
%C A118979 Negative of the determinant of a series of 3 X 3 matrices, related to Stirling's numbers of the second kind by a factor of 12 (cf. A000392, A028243).
%H A118979 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (6,-11,6).
%F A118979 Let M = {{1, 1, 1}, {2^n, 4, 2}, {3^n, 9, 3}}. Then a(n) = -Det[M]
%F A118979 a(n) = 6*(1-2^n)+2*3^n = 12*A000392(n).
%t A118979 M = {{1, 1, 1}, {2^n, 4, 2}, {3^n, 9, 3}} a = Table[ -Det[M], {n, 3, 30}]
%Y A118979 Cf. A000392, A028243.
%K A118979 nonn,easy
%O A118979 3,1
%A A118979 _Roger L. Bagula_, May 25 2006
%E A118979 Edited by _N. J. A. Sloane_, Dec 13 2007