a(n) = a(n-1) + a(n-2) + a(n-3).

Terms

a(0) =1a(1) =3a(2) =4a(3) =8a(4) =15a(5) =27a(6) =50a(7) =92a(8) =169a(9) =311a(10) =572a(11) =1052a(12) =1935a(13) =3559a(14) =6546a(15) =12040a(16) =22145a(17) =40731a(18) =74916a(19) =137792a(20) =253439a(21) =466147a(22) =857378a(23) =1576964a(24) =2900489a(25) =5334831a(26) =9812284a(27) =18047604a(28) =33194719a(29) =61054607