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

Terms

a(0) =1a(1) =-4a(2) =9a(3) =-16a(4) =25a(5) =-36a(6) =49a(7) =-64a(8) =81a(9) =-100a(10) =121a(11) =-144a(12) =169a(13) =-196a(14) =225a(15) =-256a(16) =289a(17) =-324a(18) =361a(19) =-400a(20) =441a(21) =-484a(22) =529a(23) =-576a(24) =625a(25) =-676a(26) =729a(27) =-784a(28) =841a(29) =-900