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

Terms

a(0) =1a(1) =2a(2) =2a(3) =3a(4) =6a(5) =10a(6) =15a(7) =24a(8) =40a(9) =65a(10) =104a(11) =168a(12) =273a(13) =442a(14) =714a(15) =1155a(16) =1870a(17) =3026a(18) =4895a(19) =7920a(20) =12816a(21) =20737a(22) =33552a(23) =54288a(24) =87841a(25) =142130a(26) =229970a(27) =372099a(28) =602070a(29) =974170