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 A120017 #8 Mar 10 2015 02:16:54
%S A120017 1,2,4,10,32,116,440,1708,6760,27232,111392,461536,1933024,8170400,
%T A120017 34807232,149304080,644298592,2795216576,12184415360,53338632256,
%U A120017 234393350912,1033614750080,4572427361536,20285780245120,90238113332992
%N A120017 The 2nd self-composition of A120010; g.f.: A(x) = G(G(x)), where G(x) = g.f. of A120010.
%F A120017 G.f.: A(x) = (1 - sqrt(1 - 4*x*(1-x)/(1-2*x+2*x^2) ))/2.
%e A120017 A(x) = x + 2*x^2 + 4*x^3 + 10*x^4 + 32*x^5 + 116*x^6 + 440*x^7 +...
%e A120017 G(x) = x + x^2 + x^3 + 2*x^4 + 6*x^5 + 18*x^6 + 53*x^7 + 158*x^8 +...
%e A120017 where G(x) is the g.f. of A120010 and G(G(x)) = A(x).
%o A120017 (PARI) {a(n)=polcoeff((1 - sqrt(1 - 4*x*(1-x)/(1-2*x+2*x^2+x*O(x^n)) ))/2, n)}
%Y A120017 Cf. A120010, A120018 (3rd self-composition).
%K A120017 nonn
%O A120017 1,2
%A A120017 _Paul D. Hanna_, Jun 14 2006