OFFSET
0,2
FORMULA
a(n) = 2*Sum(k=1..2*n, Sum(t=0..n-k, binomial(2*n,2*t+k)*((Sum(j=k..2*n-2*t-k, binomial(j-1,k-1)*j!*Stirling2(2*n-2*t-k,j)*(-1)^(n+j)*2^(-2*t-k+2*n-j)))*Sum(i=0..k/2, (2*i-k)^(2*t+k)*binomial(k,i)*(-1)^(k-i))))/(2^k*k!)), n>0, a(0)=1. - Vladimir Kruchinin, Jun 30 2011
a(n) ~ (2*n)! * 2^(2*n-1/2) * exp(1/Pi + 4*sqrt(n/Pi)) / (n^(3/4) * Pi^(2*n+3/4)) * (1 - (5*Pi^2-2) / (12*Pi^(3/2)*sqrt(n))). - Vaclav Kotesovec, Jan 24 2015
MATHEMATICA
nn = 20; Table[(CoefficientList[Series[E^(Sin[x]*Tan[x]), {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Jan 24 2015 *)
PROG
(Maxima)
a(n):=if n=0 then 1 else 2*sum(sum(binomial(2*n, 2*t+k)*((sum(binomial(j-1, k-1)*j!*stirling2(2*n-2*t-k, j)*(-1)^(n+j)*2^(-2*t-k+2*n-j), j, k, 2*n-2*t-k))*sum((2*i-k)^(2*t+k)*binomial(k, i)*(-1)^(k-i), i, 0, k/2)), t, 0, n-k)/(2^k*k!), k, 1, 2*n); /* Vladimir Kruchinin, Jun 30 2011 */
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Extended and signs tested by Olivier Gérard, Mar 15 1997
STATUS
approved