a(n) = Sum_{i=n-4..n-1} (-1)^i*a(i), a(1)=1, a(2)=1, a(3)=1, a(4)=1.

Terms

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