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 A179331 #2 Mar 30 2012 18:37:22
%S A179331 1,3,21,234,3540,66564,1469412,36584784,998692416,29407250880,
%T A179331 934026603840,32655607021440,1292780225168640,57672298842359040,
%U A179331 2712127097197728000,122155073614867507200,5128063415272020787200
%N A179331 E.g.f. satisfies: A(x) = (1-x)/(1-3*x) * A(x*(1-x)^2).
%F A179331 a(n) = -(-1)^n*A179330(n)/2; see A179330 for more formulas. First negative term is a(22).
%o A179331 (PARI) {a(n)=local(M=matrix(n+1, n+1, r, c, if(r>=c, polcoeff(((1-x)^2+x*O(x^n))^c,r-c))), LOG, ID=M^0); LOG=sum(m=1, n+1, -(ID-M)^m/m); -n!*LOG[n+1,1]/2}
%Y A179331 Cf. A179330.
%K A179331 nonn
%O A179331 1,2
%A A179331 _Paul D. Hanna_, Jul 21 2010
%E A179331 Corrected formula by _Paul D. Hanna_, Jul 21 2010