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

Terms

a(0) =1a(1) =1a(2) =0a(3) =0a(4) =2a(5) =3a(6) =3a(7) =5a(8) =10a(9) =16a(10) =24a(11) =39a(12) =65a(13) =105a(14) =168a(15) =272a(16) =442a(17) =715a(18) =1155a(19) =1869a(20) =3026a(21) =4896a(22) =7920a(23) =12815a(24) =20737a(25) =33553a(26) =54288a(27) =87840a(28) =142130a(29) =229971