a(n) = 1 - n^2.

Terms

a(0) =1a(1) =0a(2) =-3a(3) =-8a(4) =-15a(5) =-24a(6) =-35a(7) =-48a(8) =-63a(9) =-80a(10) =-99a(11) =-120a(12) =-143a(13) =-168a(14) =-195a(15) =-224a(16) =-255a(17) =-288a(18) =-323a(19) =-360a(20) =-399a(21) =-440a(22) =-483a(23) =-528a(24) =-575a(25) =-624a(26) =-675a(27) =-728a(28) =-783a(29) =-840