a(n) = (n+1)^n - 1.

Terms

a(0) =0a(1) =1a(2) =8a(3) =63a(4) =624a(5) =7775a(6) =117648a(7) =2097151a(8) =43046720a(9) =999999999a(10) =25937424600a(11) =743008370687