a(n) = a(n-1) + a(n-2) + a(n-3), with a(0)=1, a(1)=4, a(2)=5.

Terms

a(0) =1a(1) =4a(2) =5a(3) =10a(4) =19a(5) =34a(6) =63a(7) =116a(8) =213a(9) =392a(10) =721a(11) =1326a(12) =2439a(13) =4486a(14) =8251a(15) =15176a(16) =27913a(17) =51340a(18) =94429a(19) =173682a(20) =319451a(21) =587562a(22) =1080695a(23) =1987708a(24) =3655965a(25) =6724368a(26) =12368041a(27) =22748374a(28) =41840783a(29) =76957198