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

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =7a(7) =12a(8) =21a(9) =37a(10) =65a(11) =114a(12) =200a(13) =351a(14) =616a(15) =1081a(16) =1897a(17) =3329a(18) =5842a(19) =10252a(20) =17991a(21) =31572a(22) =55405a(23) =97229a(24) =170625a(25) =299426a(26) =525456a(27) =922111a(28) =1618192a(29) =2839729