



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



