Tribonacci numbers: a(n) = a(n-1) + a(n-2) + a(n-3) with a(0)=a(1)=a(2)=1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =5a(5) =9a(6) =17a(7) =31a(8) =57a(9) =105a(10) =193a(11) =355a(12) =653a(13) =1201a(14) =2209a(15) =4063a(16) =7473a(17) =13745a(18) =25281a(19) =46499a(20) =85525a(21) =157305a(22) =289329a(23) =532159a(24) =978793a(25) =1800281a(26) =3311233a(27) =6090307a(28) =11201821a(29) =20603361