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

Terms

a(0) =0a(1) =1a(2) =5a(3) =29a(4) =259a(5) =3129a(6) =46661a(7) =823549a(8) =16777223a(9) =387420497a(10) =10000000009a(11) =285311670621