A120574 - OEIS

A120574

G.f. satisfies: A(x) = x + x*A(x) + x*A(A(x)).

1, 2, 6, 26, 146, 978, 7454, 62882, 576914, 5687506, 59732838, 664040698, 7775333858, 95517840738, 1227175022334, 16444901577858, 229338157229154, 3321917275376098, 49890293296044806, 775682898796646810

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..20.

FORMULA

G.f. satisfies: A(x) = (1/x)*Series_Reversion( x/(1+x + x*A(x)) ).

EXAMPLE

A(x) = x + 2*x^2 + 6*x^3 + 26*x^4 + 146*x^5 + 978*x^6 + 7454*x^7 +...

A(A(x)) = x + 4*x^2 + 20*x^3 + 120*x^4 + 832*x^5 + 6476*x^6 +...

PROG

(PARI) {a(n)=local(F=x+x*O(x^n), G=F); for(i=1, n, F=x+x*F+x*subst(F, x, F)); polcoeff(F, n)}

CROSSREFS

Cf. A120575.

Sequence in context: A289312 A127116 A107404 * A333044 A178324 A002710

Adjacent sequences: A120571 A120572 A120573 * A120575 A120576 A120577

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 15 2006

STATUS

approved