a(n) = 2^n + 2*n^2 + 2*n + 1.

Terms

a(0) =2a(1) =7a(2) =17a(3) =33a(4) =57a(5) =93a(6) =149a(7) =241a(8) =401a(9) =693a(10) =1245a(11) =2313a(12) =4409a(13) =8557a(14) =16805a(15) =33249a(16) =66081a(17) =131685a(18) =262829a(19) =525049a(20) =1049417a(21) =2098077a(22) =4195317a(23) =8389713a(24) =16778417a(25) =33555733a(26) =67110269a(27) =134219241a(28) =268437081a(29) =536872653