a(n) = Sum_{d|n} (n/d)^d * binomial(d+n-1,d).

Terms

a(0) =1a(1) =7a(2) =19a(3) =91a(4) =151a(5) =1135a(6) =1765a(7) =12355a(8) =28846a(9) =157917a(10) =352837a(11) =2280955a(12) =5200469a(13) =29986201a(14) =80469589a(15) =427061795a(16) =1166803399a(17) =6211188028a(18) =17672632261a(19) =89483074521a(20) =271071666724