OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
J. W. Layman, The Hankel Transform and Some of its Properties, J. Integer Sequences, 4 (2001), #01.1.5.
FORMULA
a(n) is the permanent of the n X n matrix with 4's on the diagonal and 1's elsewhere. a(n) = Sum(k=0..n, A008290(n, k)*4^k). - Philippe Deléham, Dec 12 2003
a(n) = Sum[(n! / k!) * 3^k {k=0...n}]. - Ross La Haye, Sep 21 2004
a(n) = sum{k=0..n, k!*C(n, k)3^(n-k)}. - Paul Barry, Apr 22 2005
G.f.: hypergeom([1,1],[],x/(1-3*x))/(1-3*x). - Mark van Hoeij, Nov 08 2011
D-finite with recurrence -a(n) +(n+3)*a(n-1) +3*(1-n)*a(n-2)=0. - R. J. Mathar, Nov 14 2011. This recurrence follows from the Wilf-Zeilberger (WZ) proof technique applied to the sum: Sum[k!* C(n,k)*3^(n-k), {k=0...n}]. - T. Amdeberhan, Jul 23 2012
E.g.f.: 1/E(0) where E(k)=1-x/(1-3/(3+(k+1)/E(k+1))); (continued fraction). - Sergei N. Gladkovskii, Nov 21 2011
G.f.: 1/Q(0), where Q(k)= 1 - 3*x - x*(k+1)/(1-x*(k+1)/Q(k+1)); (continued fraction). - Sergei N. Gladkovskii, Apr 20 2013
a(n) ~ n! * exp(3). - Vaclav Kotesovec, Jun 01 2013
From Peter Bala, Sep 25 2013: (Start)
a(n) = n*a(n-1) + 3^n with a(0) = 1.
a(n) = n!*e^3 - sum {k >= 0} 3^(n + k + 1)/((n + 1)*...*(n + k + 1))
= n!*e^3 - e^3*( int {t = 0..3} t^n*exp(-t) dt )
= e^3*( int {t = 3..inf} t^n*exp(-t) dt )
= e^3*( int {t = 0..inf} t^n*exp(-t)*Heaviside(t-3) dt ),
an integral representation of a(n) as the n-th moment of a nonnegative function on the positive half-axis.
Mathar's second-order recurrence above a(n) = (n + 3)*a(n-1) - 3*(n - 1)*a(n-2) has n! as a second solution. This yields the finite continued fraction expansion a(n)/n! = 1/(1 - 3/(4 - 3/(5 - 6/(6 - ...- 3*(n - 1)/(n + 3))))) valid for n >= 2. Letting n tend to infinity gives the infinite continued fraction expansion e^3 = 1/(1 - 3/(4 - 3/(5 - 6/(6 - ...- 3*(n - 1)/(n + 3 - ...))))). (End)
G.f.: 1/Q(0), where Q(k) = 1 - 2*x*(k+2) - x^2*(k+1)^2/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Sep 30 2013
a(n) = exp(3)*Gamma(1+n,3). - Peter Luschny, Dec 18 2017
a(n) = KummerU(-n, -n, 3). - Peter Luschny, May 10 2022
MAPLE
G(x):=exp(3*x)/(1-x): g[0]:=G(x): for n from 1 to 20 do g[n]:=diff(g[n-1], x) od: x:=0: seq(g[n], n=0..20); # Zerinvary Lajos, Apr 03 2009
A053486 := n -> exp(3)*GAMMA(1+n, 3):
seq(simplify(A053486(n)), n=0..20); # Peter Luschny, Dec 18 2017
seq(simplify(KummerU(-n, -n, 3)), n = 0..20); # Peter Luschny, May 10 2022
MATHEMATICA
RecurrenceTable[{a[0]==1, a[n]== n*a[n-1] + 3^n}, a, {n, 200}] (* Vincenzo Librandi, Nov 15 2012 *)
With[{nn=20}, CoefficientList[Series[Exp[3x]/(1-x), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Aug 03 2017 *)
PROG
(PARI) x='x+O('x^66); Vec(serlaplace(exp(3*x)/(1-x))) \\ Joerg Arndt, Apr 20 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 15 2000
STATUS
approved