a(n) = (-1)^floor( (n-1) / 3 ) * F(n), where F = Fibonacci.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =-3a(5) =-5a(6) =-8a(7) =13a(8) =21a(9) =34a(10) =-55a(11) =-89a(12) =-144a(13) =233a(14) =377a(15) =610a(16) =-987a(17) =-1597a(18) =-2584a(19) =4181a(20) =6765a(21) =10946a(22) =-17711a(23) =-28657a(24) =-46368a(25) =75025a(26) =121393a(27) =196418a(28) =-317811a(29) =-514229