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 A121588 #3 Mar 30 2012 18:36:58
%S A121588 1,1,-1,3,-16,145,-2347,72498,-4459887,554300965,-139235329270,
%T A121588 70475747813447,-71685052573258824,146249172542467865074,
%U A121588 -597744865134782025119044,4890851047359454263328433041,-80078758027845307168595201926254
%N A121588 G.f.: A(x) = 1+x*(1+x*(1+x*(...(1+x*(...)^(-2^n) )...)^-4)^-2)^-1.
%C A121588 Limit |a(n)|/2^[(n-1)*(n-2)/2] = 1.97254925752982255...
%e A121588 G.f.: A(x) = 1 + x/B(x); B(x) = 1 + x/C(x)^2; C(x) = 1 + x/D(x)^4;
%e A121588 D(x) = 1 + x/E(x)^8; E(x) = 1 + x/F(x)^16; ...
%e A121588 where the respective sequences begin:
%e A121588 B=[1,1,-2,11,-112,2025,-67324,4305909,-545113744,...];
%e A121588 C=[1,1,-4,42,-836,30259,-2041616,265712044,-68214603840,...];
%e A121588 D=[1,1,-8,164,-6456,467850,-63614840,16702037652,...];
%e A121588 E=[1,1,-16,648,-50736,7358500,-2008876560,1059405119352,...];
%e A121588 F=[1,1,-32,2576,-402272,116732040,-63860549280,...].
%o A121588 (PARI) {a(n)=local(A=1+x+x*O(x^n)); for(j=0, n, A=1+x/A^(2^(n-j))); polcoeff(A, n)}
%Y A121588 Cf. A120959 (variant).
%K A121588 sign
%O A121588 0,4
%A A121588 _Paul D. Hanna_, Aug 09 2006