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A137968 G.f. satisfies A(x) = 1 + x*(1 + x*A(x)^2)^6. 6
1, 1, 6, 27, 158, 981, 6342, 42728, 295008, 2079882, 14908740, 108312873, 795836544, 5903472999, 44151306690, 332552305818, 2520416719368, 19207222744326, 147086508325056, 1131292622149352, 8735383810590486 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 0..400

FORMULA

G.f.: A(x) = 1 + x*B(x)^6 where B(x) is the g.f. of A137967.

a(n) = Sum_{k=0..n-1} C(6*(n-k),k)/(n-k) * C(2*k,n-k-1) for n>0 with a(0)=1. - Paul D. Hanna, Jun 16 2009

a(n) ~ sqrt(6*s*(1-s)*(2-3*s) / ((44*s - 24)*Pi)) / (n^(3/2) * r^n), where r = 0.1201742080825038015263858974579392344239858277873... and s = 1.572098697306844482137442690518486437859864764710... are real roots of the system of equations s = 1 + r*(1 + r*s^2)^6, 12 * r^2 * s * (1 + r*s^2)^5 = 1. - Vaclav Kotesovec, Nov 22 2017

PROG

(PARI) {a(n)=local(A=1+x*O(x^n)); for(i=0, n, A=1+x*(1+x*A^2)^6); polcoeff(A, n)}

(PARI) a(n)=if(n==0, 1, sum(k=0, n-1, binomial(6*(n-k), k)/(n-k)*binomial(2*k, n-k-1))) \\ Paul D. Hanna, Jun 16 2009

CROSSREFS

Cf. A137967, A137969; A137970, A137972, A137974.

Sequence in context: A174634 A018901 A215704 * A062512 A087297 A117336

Adjacent sequences:  A137965 A137966 A137967 * A137969 A137970 A137971

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Feb 26 2008

STATUS

approved

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Last modified January 20 01:01 EST 2022. Contains 350467 sequences. (Running on oeis4.)