a(n) = -1 - 2*n + n^2 + 2*n^3 + n^4.

Terms

a(0) =-1a(1) =1a(2) =31a(3) =137a(4) =391a(5) =889a(6) =1751a(7) =3121a(8) =5167a(9) =8081a(10) =12079a(11) =17401a(12) =24311a(13) =33097a(14) =44071a(15) =57569a(16) =73951a(17) =93601a(18) =116927a(19) =144361a(20) =176359a(21) =213401a(22) =255991a(23) =304657a(24) =359951a(25) =422449a(26) =492751a(27) =571481a(28) =659287a(29) =756841