a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 1, a(1) = 1, a(2) = 1, a(3) = -1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =-1a(4) =1a(5) =3a(6) =3a(7) =3a(8) =7a(9) =13a(10) =19a(11) =29a(12) =49a(13) =81a(14) =129a(15) =207a(16) =337a(17) =547a(18) =883a(19) =1427a(20) =2311a(21) =3741a(22) =6051a(23) =9789a(24) =15841a(25) =25633a(26) =41473a(27) =67103a(28) =108577a(29) =175683