a(n) = Bell(n)*n!!.

Terms

a(0) =1a(1) =1a(2) =4a(3) =15a(4) =120a(5) =780a(6) =9744a(7) =92085a(8) =1589760a(9) =19983915a(10) =445344000a(11) =7053735150a(12) =194162549760