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A123227 E.g.f.: 2*exp(2*x) / (3 - exp(2*x)). 5
1, 3, 12, 66, 480, 4368, 47712, 608016, 8855040, 145083648, 2641216512, 52891055616, 1155444326400, 27344999497728, 696933753434112, 19031293222127616, 554336947975618560, 17155693983744196608, 562168282464340672512, 19444889661250162262016 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..19.

FORMULA

a(n) = abs(A009362(n+1)).

a(n-1) = Sum{k, 1<=k<=n} 2^(n-k)*A028246(n,k), n>=1.

a(n) = Sum{k, 0<=k<=n} 3^k*A123125(n,k).

From Paul D. Hanna, Nov 30 2011: (Start)

a(n) = 3*A122704(n) for n>0.

a(n) = Sum_{k=0..n} (-2)^(n-k) * 3^k * Stirling2(n,k) * k!.

O.g.f.: Sum_{n>=0} 3^n * n!*x^n / Product_{k=0..n} (1+2*k*x).

O.g.f.: 1/(1 - 3*x/(1-x/(1 - 6*x/(1-2*x/(1 - 9*x/(1-3*x/(1 - 12*x/(1-4*x/(1 - 15*x/(1-5*x/(1 - ...)))))))))), a continued fraction.

(End)

a(n) ~ n! * (2/log(3))^(n+1). - Vaclav Kotesovec, Jun 24 2013

MATHEMATICA

CoefficientList[Series[2*Exp[2*x]/(3-Exp[2*x]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jun 24 2013 *)

PROG

(PARI) {a(n)=n!*polcoeff(2*exp(2*x+x*O(x^n))/(3 - exp(2*x+x*O(x^n))), n)} /* Paul D. Hanna */

(PARI) {a(n)=polcoeff(sum(m=0, n, 3^m*m!*x^m/prod(k=1, m, 1+2*k*x+x*O(x^n))), n)} /* Paul D. Hanna */

(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, (-2)^(n-k)*3^k*Stirling2(n, k)*k!)} /* Paul D. Hanna */

(Sage)

@CachedFunction

def BB(n, k, x):  # Modified Cardinal B-splines

    if n == 1: return 0 if (x < 0) or (x >= k) else 1

    return x*BB(n-1, k, x) + (n*k-x)*BB(n-1, k, x-k)

def EulerianPolynomial(n, k, x):

    if n == 0: return 1

    return add(BB(n+1, k, k*m+1)*x^m for m in (0..n))

def A123227(n) : return 3^n*EulerianPolynomial(n, 1, 1/3)

[A123227(n) for n in (0..18)]  # Peter Luschny, May 04 2013

(PARI)  x='x+O('x^66); Vec(serlaplace(2*exp(2*x)/(3-exp(2*x)))) \\ Joerg Arndt, May 06 2013

CROSSREFS

Cf. A000629, A201339, A122704, A009362, A123125, A028246.

Sequence in context: A080599 A120575 A009362 * A196556 A107713 A107103

Adjacent sequences:  A123224 A123225 A123226 * A123228 A123229 A123230

KEYWORD

nonn

AUTHOR

Philippe Deléham, Oct 06 2006

EXTENSIONS

Name changed and a(8) corrected by Paul D. Hanna, Nov 30 2011

STATUS

approved

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Last modified December 22 21:10 EST 2014. Contains 252372 sequences.