OFFSET
0,2
MAPLE
b := proc(n) option remember; if n = 0 then 2 else
add(doublefactorial(2*k-1)*b(n-k), k=1..n) fi end:
a := n -> if n = 0 then return 1 else b(n) end: seq(a(n), n=0..20);
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Dec 07 2018
STATUS
approved