OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..100
FORMULA
a(n) = Sum_{k=0..n} binomial(n,k)*S(2*k,k).
a(n) ~ exp(c*(2-c)/4) * StirlingS2(2*n,n) ~ 2^(2*n-1/2)*n^(n-1/2)/(sqrt(Pi*(1-c))*exp(n-c*(2-c)/4)*(c*(2-c))^n), where c = - LambertW(-2/exp(2)) = 0.406375739959959907676958... - Vaclav Kotesovec, Jan 02 2013
O.g.f.: Sum_{n>=0} n^(2*n)/n! * x^n/(1-x)^(n+1) * exp(-n^2*x/(1-x)). - Paul D. Hanna, Jan 02 2013
MAPLE
seq(sum(binomial(n, k)*combinat[stirling2](2*k, k), k=0..n), n=0..12);
MATHEMATICA
Table[Sum[Binomial[n, k]StirlingS2[2k, k], {k, 0, n}], {n, 0, 16}]
PROG
(Maxima) makelist(sum(binomial(n, k)*stirling2(2*k, k), k, 0, n), n, 0, 12);
(PARI) a(n)=polcoeff(sum(m=0, n, m^(2*m)/m!*x^m/(1-x)^(m+1)*exp(-m^2*x/(1-x+x*O(x^n)))), n)
for(n=0, 20, print1(a(n), ", ")) \\ Paul D. Hanna, Jan 02 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emanuele Munarini, Mar 12 2011
STATUS
approved