OFFSET
0,2
FORMULA
a(n) = Sum_{k=0..n} binomial(n,k)*s(2*k,k)*s(2*n-2*k,n-k).
MAPLE
seq(sum(binomial(n, k)*abs(combinat[stirling1](2*k, k))*abs(combinat[stirling1](2*(n-k), n-k)), k=0..n), n=0..12);
MATHEMATICA
Table[Sum[Binomial[n, k]Abs[StirlingS1[2k, k]]Abs[StirlingS1[2n - 2k, n - k]], {k, 0, n}], {n, 0, 15}]
PROG
(Maxima) makelist(sum(binomial(n, k)*abs(stirling1(2*k, k))*abs(stirling1(2*n-2*k, n-k)), k, 0, n), n, 0, 12);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emanuele Munarini, Mar 12 2011
STATUS
approved