a(n) = n! * Sum_{d|n} 1/(d-1)!.

Terms

a(0) =1a(1) =4a(2) =9a(3) =52a(4) =125a(5) =1806a(6) =5047a(7) =87368a(8) =544329a(9) =7408810a(10) =39916811a(11) =1281329292a(12) =6227020813a(13) =174477663374