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A052897 E.g.f.: exp(2*x/(1-x)). 11
1, 2, 8, 44, 304, 2512, 24064, 261536, 3173888, 42483968, 621159424, 9841950208, 167879268352, 3065723549696, 59651093528576, 1231571119812608, 26883546193002496, 618463501807058944 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Previous name was: A simple grammar.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 873

N. J. A. Sloane, Transforms

FORMULA

E.g.f.: exp(2*x/(1-x)). - Vladeta Jovovic, Jan 04 2001

Recurrence: {a(0)=1, a(1)=2, (n^2+n)*a(n)+(-4-2*n)*a(n+1)+a(n+2)}.

LAH transform of A000079: a(n) = Sum_{k=0..n) 2^k*n!/k!*binomial(n-1, k-1). - Vladeta Jovovic, Oct 17 2003

a(n)=n!*L(n,-1,-2) - Karol A. Penson, Oct 16 2006 [Here L(n,a,x) is the n-th generalized Laguerre polynomial with parameter a, evaluated at x. L(n,a,x) is 1 if n=0, a+1-x if n=1 and otherwise (2*n+a-1-x)/n*L(n-1,a,x)-(n+a-1)/n*L(n-2,a,x). - Peter Luschny, Nov 20 2011]

a(n) ~ 2^(-1/4)*exp(2*sqrt(2*n)-n-1)*n^(n-1/4). - Vaclav Kotesovec, Oct 09 2012

E.g.f.: 1 + 2*x/((1-x)*T(0) - x), where T(k) = 4*k+1 + x^2/((4*k+3)*(1-x)^2 + x^2/T(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Nov 30 2013

E.g.f.: exp(Sum_{k>=1} 2*x^k). - Vaclav Kotesovec, Mar 07 2015

a(n) = Sum_{k=0..n} binomial(n,k)*l(k)*l(n-k), where l(m) = A000262(m). - Emanuele Munarini, Aug 31 2017

MAPLE

L := proc(n, a, x) if n=0 then 1 elif n=1 then a+1-x else (2*n+a-1-x)/n*L(n-1, a, x) - (n+a-1)/n*L(n-2, a, x) fi end: A052897 := n -> n!*L(n, -1, -2): seq(A052897(n), n=0..17); # Peter Luschny, Nov 20 2011

spec := [S, {B=Set(C), C=Sequence(Z, 1 <= card), S=Prod(B, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

MATHEMATICA

Range[0, 19]! CoefficientList[ Series[E^(2*x/(1 - x)), {x, 0, 19}], x] - Zerinvary Lajos, Mar 21 2007

PROG

(PARI) a=Vec(exp(2*x/(1-x))); for(n=2, #a-1, a[n+1]*=n!); a \\ Charles R Greathouse IV, Nov 20 2011

(MAGMA) m:=25; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!(Exp(2*x/(1 - x)))); [Factorial(n-1)*b[n]: n in [1..m]]; // G. C. Greubel, May 15 2018

CROSSREFS

Row sums of A059110.

Cf. A000262, A025168, A255806.

Sequence in context: A321942 A124467 A075792 * A137984 A191810 A172109

Adjacent sequences:  A052894 A052895 A052896 * A052898 A052899 A052900

KEYWORD

easy,nonn

AUTHOR

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

EXTENSIONS

New name using e.g.f., Vaclav Kotesovec, Feb 25 2014

STATUS

approved

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Last modified August 19 04:34 EDT 2019. Contains 326109 sequences. (Running on oeis4.)