a(0) = -1 and a(n) = (-1)^(n+1)*(3*n^2 - n + 4)/2 for n >= 1.

Terms

a(0) =-1a(1) =3a(2) =-7a(3) =14a(4) =-24a(5) =37a(6) =-53a(7) =72a(8) =-94a(9) =119a(10) =-147a(11) =178a(12) =-212a(13) =249a(14) =-289a(15) =332a(16) =-378a(17) =427a(18) =-479a(19) =534a(20) =-592a(21) =653a(22) =-717a(23) =784a(24) =-854a(25) =927a(26) =-1003a(27) =1082a(28) =-1164a(29) =1249