a(n) = a(n-1) + a(n-3) + a(n-4), where a(0) = 2, a(1) = 1, a(2) = 0, a(3) = 2.

Terms

a(0) =2a(1) =1a(2) =0a(3) =2a(4) =5a(5) =6a(6) =8a(7) =15a(8) =26a(9) =40a(10) =63a(11) =104a(12) =170a(13) =273a(14) =440a(15) =714a(16) =1157a(17) =1870a(18) =3024a(19) =4895a(20) =7922a(21) =12816a(22) =20735a(23) =33552a(24) =54290a(25) =87841a(26) =142128a(27) =229970a(28) =372101a(29) =602070