a(n) = 24*5^n - 60*4^n + 50*3^n - 15*2^n + 1.

Terms

a(0) =0a(1) =1a(2) =31a(3) =391a(4) =3451a(5) =25231a(6) =164731a(7) =999391a(8) =5767051a(9) =32122831a(10) =174397531a(11) =929043391a(12) =4879252651a(13) =25349936431a(14) =130617150331a(15) =668714319391