G.f. Sum_{n=-oo..+oo} (x^n - x)^(n+1).

Terms

a(0) =2a(1) =-1a(2) =1a(3) =-1a(4) =4a(5) =-3a(6) =-1a(7) =-1a(8) =13a(9) =-1a(10) =-7a(11) =-10a(12) =10a(13) =-1a(14) =22a(15) =-1a(16) =10a(17) =-23a(18) =-25a(19) =-1a(20) =43a(21) =-1a(22) =50a(23) =-36a(24) =14a(25) =-1a(26) =-19a(27) =-26a(28) =16a(29) =-55