OFFSET
0,2
COMMENTS
This sequence arises in the normal ordering problem the exponential of square of boson number operator.
FORMULA
MATHEMATICA
Array[BellB[2 #] (2 # - 1)!! &, 13, 0] (* Michael De Vlieger, Dec 24 2017 *)
PROG
(PARI) a(n)=round(exp(-1)*suminf(k=0, k^(2*n)/k!))*(2*n)!/(2^n*n!) \\ Charles R Greathouse IV, Nov 06 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Karol A. Penson, Nov 03 2004
STATUS
approved