a(n) = a(n-1) - a(n-3) with a(1)=0, a(2)=0, a(3)=1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =1a(5) =0a(6) =-1a(7) =-2a(8) =-2a(9) =-1a(10) =1a(11) =3a(12) =4a(13) =3a(14) =0a(15) =-4a(16) =-7a(17) =-7a(18) =-3a(19) =4a(20) =11a(21) =14a(22) =10a(23) =-1a(24) =-15a(25) =-25a(26) =-24a(27) =-9a(28) =16a(29) =40