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

Terms

a(0) =0a(1) =2a(2) =-3a(3) =6a(4) =-8a(5) =12a(6) =-15a(7) =20a(8) =-24a(9) =30a(10) =-35a(11) =42a(12) =-48a(13) =56a(14) =-63a(15) =72a(16) =-80a(17) =90a(18) =-99a(19) =110a(20) =-120a(21) =132a(22) =-143a(23) =156a(24) =-168a(25) =182a(26) =-195a(27) =210a(28) =-224a(29) =240