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 A172401 #2 Mar 30 2012 18:37:21
%S A172401 1,1,2,6,32,332,6928,292334,24875760,4254812880,1459549877168,
%T A172401 1002824206109916,1379081986798078000,3794489305535947254732,
%U A172401 20884859614892223147785056,229923086002576723635638394810
%N A172401 G.f.: 1/(1-x) = Sum_{n>=0} a(n)*x^n/(1+x)^(2^n-1).
%F A172401 Column 0 of triangle A172400.
%e A172401 1/(1-x) = 1 + x/(1+x) + 2*x^2/(1+x)^3 + 6*x^3/(1+x)^7 + 32*x^4/(1+x)^15 +...
%o A172401 (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-1)),n))}
%Y A172401 Cf. A172400, A172402, A172403.
%K A172401 nonn
%O A172401 0,3
%A A172401 _Paul D. Hanna_, Feb 01 2010