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 A172403 #2 Mar 30 2012 18:37:21
%S A172403 1,1,5,51,1059,44620,3795202,649054326,222639357434,152968659433948,
%T A172403 210361428050679489,578800452225641673965,3185715127946958245708501,
%U A172403 35071788327149162320178667272,772254422082165524711277630023576
%N A172403 G.f.: 1/(1-x) = Sum_{n>=0} a(n)*x^n/(1+x)^(2^(n+2)-4).
%F A172403 Column 2 of triangle A172400.
%e A172403 1/(1-x) = 1 + x/(1+x)^4 + 5*x^2/(1+x)^12 + 51*x^3/(1+x)^28 + 1059*x^4/(1+x)^60 +...
%o A172403 (PARI) {a(n)=if(n==0,1,polcoeff(-(1-x)*sum(m=0,n-1,a(m)*x^m/(1+x +x*O(x^n))^(2^(m+2)-4)),n))}
%Y A172403 Cf. A172400, A172401, A172402.
%K A172403 nonn
%O A172403 0,3
%A A172403 _Paul D. Hanna_, Feb 01 2010