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

Terms

a(0) =1a(1) =4a(2) =12a(3) =76a(4) =630a(5) =7968a(6) =117656a(7) =2105416a(8) =43048917a(9) =1000781420a(10) =25937424612a(11) =743130116112