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

Terms

a(0) =-1a(1) =2a(2) =3a(3) =7a(4) =31a(5) =261a(6) =3131a(7) =46663a(8) =823551a(9) =16777225a(10) =387420499a(11) =10000000011a(12) =285311670623