a[1] = 1, a[2] = 2, a[3] = 2; a[n] = 3*a[abs[a[n-2]]] - 3*a[n-abs[a[n-2]]] + a[n-3].

Terms

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