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A215115 G.f. A(x) satisfies: A(A(A(x))) = G(x) where G(x) = x + 2*x^2 + x*G(G(G(x))) is the g.f. of A215114. 4
1, 1, 1, 19, 163, 2269, 34093, 584767, 10989271, 224143489, 4910384809, 114714875755, 2841991084747, 74337591206629, 2045557726962949, 59036247882081847, 1782385894711138303, 56166016733387381449, 1843556640469175481985, 62915735570546535121891 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

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

FORMULA

a(n) == 1 (mod 18).

EXAMPLE

G.f.: A(x) = x + x^2 + x^3 + 19*x^4 + 163*x^5 + 2269*x^6 + 34093*x^7 +...

Let G(x) = A(A(A(x))):

G(x) = x + 3*x^2 + 9*x^3 + 81*x^4 + 891*x^5 + 11907*x^6 + 184437*x^7 +...

such that G(x) = x + 2*x^2 + x*G(G(G(x))):

G(G(G(x))) = x + 9*x^2 + 81*x^3 + 891*x^4 + 11907*x^5 + 184437*x^6 +...

PROG

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

for(j=1, n+1, A=round((2*A+subst(B, x, serreverse(subst(A, x, A+x*O(x^n)))))/3));; polcoeff(A, n)}

for(n=1, 31, print1(a(n), ", "))

CROSSREFS

Cf. A215114, A213009, A215117, A215119.

Sequence in context: A159682 A197500 A212850 * A142128 A158966 A038864

Adjacent sequences:  A215112 A215113 A215114 * A215116 A215117 A215118

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Aug 03 2012

STATUS

approved

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Last modified April 18 06:48 EDT 2019. Contains 322209 sequences. (Running on oeis4.)