a(n) = n! * Sum_{d|n} (n/d)^d / d!.

Terms

a(0) =1a(1) =5a(2) =19a(3) =145a(4) =601a(5) =8521a(6) =35281a(7) =672001a(8) =4898881a(9) =82615681a(10) =439084801a(11) =21138606721a(12) =80951270401