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A301312 G.f.: Sum_{n>=0} ( (1+x)^n + (1+2*x)^n )^n / 3^(n+1). 3
1, 15, 818, 75237, 9704172, 1610219061, 326647152627, 78322576680405, 21671112063131181, 6796070676619188507, 2382079473846244973676, 922852837565535061715211, 391585126460697011112411576, 180608810765895380940822677853, 89966485333525032479641295540142, 48135006154108946423894447901622257, 27530139433795469892705229664410072563, 16761420605156187498505881406969283279001 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Paul D. Hanna, Table of n, a(n) for n = 0..100

FORMULA

G.f.: Sum_{n>=0} Sum_{k=0..n} binomial(n,k) * (1+x)^(n*(n-k)) * (1+2*x)^(n*k) / 3^(n+1).

G.f.: Sum_{n>=0} [ Sum_{k=0..n} binomial(n,k) * (1+2^k)*x^k ]^n / 3^(n+1).

a(n) ~ c * d^n * n! / sqrt(n), where d = 36.9010493125536756798917509741716959... and c = 0.4484222753815457836094869794957853521... - Vaclav Kotesovec, Oct 10 2020

EXAMPLE

G.f.: A(x) = 1 + 15*x + 818*x^2 + 75237*x^3 + 9704172*x^4 + 1610219061*x^5 + 326647152627*x^6 + 78322576680405*x^7 + 21671112063131181*x^8 + ...

such that

A(x) = 1/3  +  ((1+x) + (1+2*x))/3^2  +  ((1+x)^2 + (1+2*x)^2)^2/3^3  +  ((1+x)^3 + (1+2*x)^3)^3/3^4  +  ((1+x)^4 + (1+2*x)^4)^4/3^5  +  ((1+x)^5 + (1+2*x)^5)^5/3^6  + ... + ((1+x)^n + (1+2*x)^n)^n / 3^(n+1) + ...

Equivalently,

A(x) = 1/3 + (2 + 3*x)/3^2 + (2 + 6*x + 5*x^2)^2/3^3 + (2 + 9*x + 15*x^2 + 9*x^3)^3/3^4 + (2 + 12*x + 30*x^2 + 36*x^3 + 17*x^4)^4/3^5 + (2 + 15*x + 50*x^2 + 90*x^3 + 85*x^4 + 33*x^5)^5/3^6 + ...

CROSSREFS

Cf. A301307, A301310.

Sequence in context: A211104 A279493 A183821 * A230181 A187803 A261828

Adjacent sequences:  A301309 A301310 A301311 * A301313 A301314 A301315

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Mar 18 2018

STATUS

approved

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Last modified January 23 07:52 EST 2022. Contains 350510 sequences. (Running on oeis4.)