A weighted tribonacci, (1,2,4).

Terms

a(0) =1a(1) =3a(2) =9a(3) =19a(4) =49a(5) =123a(6) =297a(7) =739a(8) =1825a(9) =4491a(10) =11097a(11) =27379a(12) =67537a(13) =166683a(14) =411273a(15) =1014787a(16) =2504065a(17) =6178731a(18) =15246009a(19) =37619731a(20) =92826673a(21) =229050171a(22) =565182441a(23) =1394589475a(24) =3441155041a(25) =8491063755a(26) =20951731737a(27) =51698479411a(28) =127566197905a(29) =314770083675