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 A121399 G.f. satisfies: A(x) = G(x)*A(x^2*G(x)) where G(x) is the g.f. of the Motzkin numbers (A001006): G = (1 + x*G + x^2*G^2). 2
 1, 1, 3, 6, 17, 42, 114, 302, 827, 2263, 6275, 17468, 48967, 137834, 389738, 1105861, 3148240, 8987989, 25726635, 73808069, 212196040, 611219900, 1763659860, 5097131364, 14752847173, 42757853357, 124080269331, 360493591232 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Equals column 0 of triangle A121400. LINKS EXAMPLE A(x) = 1 + x + 3*x^2 + 6*x^3 + 17*x^4 + 42*x^5 + 114*x^6 +... The g.f. of the Motzkin numbers begins: G(x) = 1 + x + 2*x^2 + 4*x^3 + 9*x^4 + 21*x^5 + 51*x^6 + 127*x^7 +... PROG (PARI) {a(n)=local(F=1+x+x^2, G=serreverse(x/(F+x^2*O(x^n)))/x, H=1+x, A); for(i=0, n, H=G*subst(H, x, x^2*G)+x^2*O(x^n)); A=(x*H-y*subst(H, x, x*y))/(x*subst(F, x, y)-y); polcoeff(polcoeff(A, n, x), 0, y)} CROSSREFS Cf. A121400 (triangle), A121398 (main diagonal), A001006 (Motzkin). Sequence in context: A275057 A320807 A089264 * A212421 A238428 A232771 Adjacent sequences:  A121396 A121397 A121398 * A121400 A121401 A121402 KEYWORD nonn AUTHOR Paul D. Hanna, Jul 27 2006 STATUS approved

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Last modified May 9 20:41 EDT 2021. Contains 343746 sequences. (Running on oeis4.)