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

Terms

a(0) =-1a(1) =-3a(2) =-1a(3) =11a(4) =39a(5) =89a(6) =167a(7) =279a(8) =431a(9) =629a(10) =879a(11) =1187a(12) =1559a(13) =2001a(14) =2519a(15) =3119a(16) =3807a(17) =4589a(18) =5471a(19) =6459a(20) =7559a(21) =8777a(22) =10119a(23) =11591a(24) =13199a(25) =14949a(26) =16847a(27) =18899a(28) =21111a(29) =23489