a(0) = a(1) = a(2) = 1; thereafter a(n) = a(n-1) - (-1)^n*a(n-2) + 2*a(n-3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =3a(6) =4a(7) =7a(8) =9a(9) =10a(10) =15a(11) =23a(12) =28a(13) =35a(14) =53a(15) =74a(16) =91a(17) =123a(18) =180a(19) =239a(20) =305a(21) =426a(22) =599a(23) =783a(24) =1036a(25) =1451a(26) =1981a(27) =2602a(28) =3523a(29) =4883