a(0) = 0, a(n) = n + a(n-1) if n is odd, a(n) = -3*a(n/2) if n is even.

Terms

a(0) =0a(1) =1a(2) =-3a(3) =0a(4) =9a(5) =14a(6) =0a(7) =7a(8) =-27a(9) =-18a(10) =-42a(11) =-31a(12) =0a(13) =13a(14) =-21a(15) =-6a(16) =81a(17) =98a(18) =54a(19) =73a(20) =126a(21) =147a(22) =93a(23) =116a(24) =0a(25) =25a(26) =-39a(27) =-12a(28) =63a(29) =92