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A196556 O.g.f.: Sum_{n>=0} 3*(n+3)^(n-1) * x^n / Product_{k=1..n} (1+k*x). 3
1, 3, 12, 66, 483, 4476, 50454, 671649, 10328118, 180341094, 3527385345, 76435691250, 1818255212490, 47118807865863, 1321527658352016, 39889359465259446, 1289471521115731611, 44450463108654209136, 1627806562174453037802 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..18.

FORMULA

E.g.f.: exp(-3*LambertW(exp(-x)-1)).

a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*3*(k+3)^(k-1).

E.g.f. A(x) = G(x)^3 where G(x) = e.g.f. of A058864, which is the number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4.

a(n) ~ 3*sqrt(exp(1)-1) * n^(n-1) / (exp(n-3) * (1-log(exp(1)-1))^(n-1/2)). - Vaclav Kotesovec, Jul 09 2013

EXAMPLE

O.g.f.: A(x) = 1 + 3*x + 12*x^2 + 66*x^3 + 483*x^4 + 4476*x^5 +...

where the o.g.f. is given by:

A(x) = 1 + 3*4^0*x/(1+x) + 3*5^1*x^2/((1+x)*(1+2*x)) + 3*6^2*x^3/((1+x)*(1+2*x)*(1+3*x)) + 3*7^3*x^4/((1+x)*(1+2*x)*(1+3*x)*(1+4*x)) +...

E.g.f.: A(x) = 1 + 3*x + 12*x^2/2! + 66*x^3/3! + 483*x^4/4! + 4476*x^5/5! +...

where the e.g.f. is given by:

A(x)^(1/3) = 1 + x + 2*x^2/2! + 8*x^3/3! + 49*x^4/4! + 402*x^5/5! + 4144*x^6/6! +...+ A058864(n)*x^n/n! +...

MATHEMATICA

CoefficientList[Series[E^(-3*LambertW[E^(-x)-1]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jul 09 2013 *)

PROG

(PARI) {a(n)=polcoeff(sum(m=0, n, 3*(m+3)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}

(PARI) /* E.g.f. = G(x)^3 where G(x) = e.g.f. of A058864 */

{A058864(n)=polcoeff(sum(m=0, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}

{a(n)=n!*polcoeff(sum(k=0, n, A058864(k)*x^k/k!+x*O(x^n))^3, n)}

(PARI) {Stirling2(n, k)=if(k<0|k>n, 0, sum(i=0, k, (-1)^i*binomial(k, i)/k!*(k-i)^n))}

{a(n)=sum(k=0, n, (-1)^(n-k)*Stirling2(n, k)*3*(k+3)^(k-1))}

CROSSREFS

Cf. A058864, A196555, A196557.

Sequence in context: A120575 A009362 A123227 * A107713 A289539 A256125

Adjacent sequences:  A196553 A196554 A196555 * A196557 A196558 A196559

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Oct 03 2011

STATUS

approved

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Last modified June 13 05:33 EDT 2021. Contains 344981 sequences. (Running on oeis4.)