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 A136168 #2 Mar 30 2012 18:37:08
%S A136168 1,3,16,120,1140,12972,171216,2571912,43429680,816108048,16894168704,
%T A136168 381536713152,9332214825024,246215663789760,6984603724315392,
%U A136168 211834855804295808,6819603388970206464,232454553855108173568
%N A136168 a(n) = (n-1)!*Sum_{i=1..n-1} (-1)^(i+1)*A027907(n-i+2,i+1)*a(n-i)/(n-i)! for n>0 with a(0)=1, where A027907 is the triangle of trinomial coefficients.
%F A136168 E.g.f. satisfies: A(x) = (1-x+x^2)^2/(1-2x)*A(x-x^2+x^3).
%e A136168 E.g.f.: A(x) = 1 + 3x + 16x^2/2! + 120x^3/3! + 1140x^4/4! + 12972x^5/5! +...
%o A136168 (PARI) {a(n)=if(n<0,0,if(n==0,1,(n-1)!*sum(i=1,n,(-1)^(i+1)*polcoeff((1+x+x^2)^(n-i+2),i+1)*a(n-i)/(n-i)!)))}
%Y A136168 Cf. A027907; A005119 (variant).
%K A136168 nonn
%O A136168 0,2
%A A136168 _Paul D. Hanna_, Dec 27 2007, Jan 24 2008