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

0,3

Links

Table of n, a(n) for n=0..20.

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.

Prog

(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)}

Crossrefs

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

Sequence in context: A211248 A346414 A028475 * A320615 A316298 A291531

Adjacent sequences: A128324 A128325 A128326 * A128328 A128329 A128330

Keyword

nonn

Author

Paul D. Hanna, Mar 11 2007

Status

approved