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 A171209 #10 Apr 02 2025 16:10:08
%S A171209 1,7,119,3955,247093,29355725,6770018269,3075928905505,
%T A171209 2774997766597238,4989660046676105752,17913062958150482828608,
%U A171209 128508635121001835101510976,1843071985575998120371392747776,52855626540938653363337299348546560,3031270298538159379928340759759663584000
%N A171209 G.f. satisfies: A(x) = (1 + x*A(2x))^7.
%F A171209 Self-convolution 7th power of A171208 where a(n) = A171208(n+1)/2^n for n>=0.
%t A171209 terms = 15; A[_] = 0; Do[A[x_] = (1+x*A[2x])^7 + O[x]^terms // Normal, terms]; CoefficientList[A[x], x] (* _Stefano Spezia_, Apr 02 2025 *)
%o A171209 (PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=0, n, A=(1+x*subst(A, x, 2*x))^7); polcoeff(A, n)}
%Y A171209 Cf. A135868, A171200-A171207, A171208, A171210-A171211.
%K A171209 nonn
%O A171209 0,2
%A A171209 _Paul D. Hanna_, Dec 05 2009
%E A171209 a(13)-a(14) from _Stefano Spezia_, Apr 02 2025