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

Terms

a(0) =1a(1) =4a(2) =9a(3) =76a(4) =125a(5) =4686a(6) =5047a(7) =389768a(8) =1995849a(9) =62445610a(10) =39916811a(11) =23574862092a(12) =6227020813