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 A180716 #4 Apr 07 2012 22:10:44
%S A180716 1,1,4,35,524,11844,374544,15740121,846918340,56716282700,
%T A180716 4622924730800,450422314335500,51679784091622960,6895215281303487760,
%U A180716 1058342987968671733824,185145713675921057952219,36616521252754210909572684,8128356026325692474893812996
%N A180716 G.f.: 1 = Sum_{n>=0} a(n)*x^n * Sum_{k=0..n+1} C(n+1,k)^2*(-x)^k.
%C A180716 Compare g.f. to a g.f. of the Catalan numbers (A000108):
%C A180716 1 = Sum_{n>=0} A000108(n)*x^n * Sum_{k=0..n+1} C(n+1,k)*(-x)^k.
%e A180716 G.f.: 1 = 1*(1-x) + 1*x*(1-2^2*x+x^2) + 4*x^2*(1-3^2*x+3^2*x^2-x^3) + 35*x^3*(1-4^2*x+6^2*x^2-4^2*x^3+x^4) + 524*x^4*(1-5^2*x+10^2*x^2-10^2*x^3+5^2*x^4-x^5) +...
%o A180716 (PARI) {a(n)=if(n==0,1,-polcoeff(sum(m=0,n-1,a(m)*x^m*sum(k=0,m+1,binomial(m+1,k)^2*(-x)^k)+x*O(x^n)),n))}
%Y A180716 Cf. A209440.
%K A180716 nonn
%O A180716 0,3
%A A180716 _Paul D. Hanna_, Sep 28 2010