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

Terms

a(0) =0a(1) =-1a(2) =2a(3) =-3a(4) =4a(5) =-5a(6) =6a(7) =-7a(8) =8a(9) =-9a(10) =10a(11) =-11a(12) =12a(13) =-13a(14) =14a(15) =-15a(16) =16a(17) =-17a(18) =18a(19) =-19a(20) =20a(21) =-21a(22) =22a(23) =-23a(24) =24a(25) =-25a(26) =26a(27) =-27a(28) =28a(29) =-29