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 A135868 #9 Apr 02 2025 16:10:15
%S A135868 1,2,9,80,1368,45344,2952208,381005824,97928967168,50238812700672,
%T A135868 51495089926791168,105513593089512439808,432289346894817079853056,
%U A135868 3541746937174189008054386688,58031524865557213409213540204544,1901635048957282075182110362797342720,124627456377710926240825658971690792648704
%N A135868 G.f. A(x) = (1 + x*A(2*x))^2.
%C A135868 Self-convolution of A135867 such that A135867(n+1) = 2^n*a(n).
%t A135868 terms = 17; A[_] = 0; Do[A[x_] = (1 + x*A[2x])^2 + O[x]^terms // Normal, terms]; CoefficientList[A[x], x] (* _Stefano Spezia_, Apr 02 2025 *)
%o A135868 (PARI) {a(n)=local(A=1+x+x*O(x^n));for(i=0,n,A=1+x*subst(A,x,2*x)^2);polcoeff(A^2,n)}
%Y A135868 Cf. A135867.
%K A135868 nonn
%O A135868 0,2
%A A135868 _Paul D. Hanna_, Dec 02 2007
%E A135868 a(15)-a(16) from _Stefano Spezia_, Apr 02 2025