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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =4a(5) =5a(6) =8a(7) =12a(8) =17a(9) =25a(10) =37a(11) =54a(12) =79a(13) =116a(14) =170a(15) =249a(16) =365a(17) =535a(18) =784a(19) =1149a(20) =1684a(21) =2468a(22) =3617a(23) =5301a(24) =7769a(25) =11386a(26) =16687a(27) =24456a(28) =35842a(29) =52529