A128327 Row 2 of table A128325.

1, 1, 4, 20, 114, 712, 4772, 33896, 253102, 1975610, 16054568, 135413280, 1182664740, 10675334958, 99437919664, 954581258020, 9433732288486, 95883201181772, 1001411775057322, 10738668800872594, 118151145186400408

Offset: 0

Author

Paul D. Hanna, Mar 11 2007

Keywords

• nonn

Crossrefs

Cf. A030266; A128325 (table), A128326 (row 1), A128328 (row 3), A128329 (main diagonal).

Programs

PARI

{a(n)=local(A=1+x,B);for(i=0,n,A=1+x*A*subst(A,x,x*A+x*O(x^n))); B=A;for(i=1,2,B=subst(B,x,x*A+x*O(x^n)));polcoeff(B,n)}

Formula

G.f.: A(x) = 1 + G(G(G(G(x)))) = B(G(x)), where B(x) is the g.f. of A128326 and G(x) = x + x*G(G(x)) is the g.f. of A030266.