a(n) = 3/8 + (3/8)*(-1)^n + ((n+1)/4)*(-1)^(n+1) + ((n+2)*(n+1)/4)*(-1)^(n+2).

Terms

a(0) =1a(1) =-1a(2) =3a(3) =-4a(4) =7a(5) =-9a(6) =13a(7) =-16a(8) =21a(9) =-25a(10) =31a(11) =-36a(12) =43a(13) =-49a(14) =57a(15) =-64a(16) =73a(17) =-81a(18) =91a(19) =-100a(20) =111a(21) =-121a(22) =133a(23) =-144a(24) =157a(25) =-169a(26) =183a(27) =-196a(28) =211a(29) =-225