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

Terms

a(0) =1a(1) =1a(2) =1a(3) =5a(4) =9a(5) =13a(6) =17a(7) =25a(8) =37a(9) =53a(10) =73a(11) =101a(12) =141a(13) =197a(14) =273a(15) =377a(16) =521a(17) =721a(18) =997a(19) =1377a(20) =1901a(21) =2625a(22) =3625a(23) =5005a(24) =6909a(25) =9537a(26) =13165a(27) =18173a(28) =25085a(29) =34625