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

Terms

a(0) =2a(1) =3a(2) =4a(3) =9a(4) =16a(5) =29a(6) =54a(7) =99a(8) =182a(9) =335a(10) =616a(11) =1133a(12) =2084a(13) =3833a(14) =7050a(15) =12967a(16) =23850a(17) =43867a(18) =80684a(19) =148401a(20) =272952a(21) =502037a(22) =923390a(23) =1698379a(24) =3123806a(25) =5745575a(26) =10567760a(27) =19437141a(28) =35750476a(29) =65755377