a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) - a(n-4), n>=4; a(0) = 1, a(1) = 1, a(2) = 2, a(3) = 3.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =3a(5) =1a(6) =-5a(7) =-18a(8) =-41a(9) =-75a(10) =-115a(11) =-143a(12) =-118a(13) =35a(14) =431a(15) =1213a(16) =2499a(17) =4254a(18) =6047a(19) =6665a(20) =3609a(21) =-7375a(22) =-32334a(23) =-77933a(24) =-147781a(25) =-234503a(26) =-305765a(27) =-283634a(28) =-20329a(29) =718653