OFFSET
0,2
COMMENTS
a(n) = 2^n*A002720(n).
FORMULA
E.g.f.: (1/(1-2x))*exp(2x/(1-2x)). - corrected by Vaclav Kotesovec, Sep 26 2013
a(n) = 2^n*n!*sum{k=0..n, C(n,k)/k!}.
Conjecture: a(n) -4*n*a(n-1) +4*(n-1)^2*a(n-2)=0. - R. J. Mathar, Nov 14 2011
a(n) ~ 2^(n-1/2)*n^(n+1/4)*exp(2*sqrt(n)-n-1/2) * (1 + 31/(48*sqrt(n))). - Vaclav Kotesovec, Sep 26 2013
a(n) = 2^n*n!*LaguerreL(n, -1). - Peter Luschny, Jan 19 2020
MAPLE
a := n -> 2^n*n!*LaguerreL(n, -1):
seq(simplify(a(n)), n=0..18); # Peter Luschny, Jan 19 2020
MATHEMATICA
Table[2^n*n!*Sum[Binomial[n, k]/k!, {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Sep 26 2013 *)
CoefficientList[Series[(1/(1-2*x))*E^(2*x/(1-2*x)), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Sep 26 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Apr 28 2007
EXTENSIONS
Error in definition corrected by Vaclav Kotesovec, Sep 26 2013
STATUS
approved