G.f.: imaginary part of 1/(1 - i*x - i*x^2) where i=sqrt(-1).

Terms

a(0) =0a(1) =1a(2) =1a(3) =-1a(4) =-3a(5) =-2a(6) =4a(7) =9a(8) =3a(9) =-15a(10) =-25a(11) =0a(12) =52a(13) =65a(14) =-27a(15) =-169a(16) =-155a(17) =158a(18) =520a(19) =321a(20) =-681a(21) =-1519a(22) =-481a(23) =2560a(24) =4200a(25) =-79a(26) =-8839a(27) =-10881a(28) =4797a(29) =28638