a(n) = a(n-1) + a(n-2) + a(n-4), with a(1)=1, a(2)=1, a(3)=3, a(4)=6.

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =10a(5) =17a(6) =30a(7) =53a(8) =93a(9) =163a(10) =286a(11) =502a(12) =881a(13) =1546a(14) =2713a(15) =4761a(16) =8355a(17) =14662a(18) =25730a(19) =45153a(20) =79238a(21) =139053a(22) =244021a(23) =428227a(24) =751486a(25) =1318766a(26) =2314273a(27) =4061266a(28) =7127025a(29) =12507057