a(n) = 3*a(n-1) - 2*a(n-2) + a(n-3), n > 3.

Terms

a(0) =0a(1) =3a(2) =6a(3) =13a(4) =30a(5) =70a(6) =163a(7) =379a(8) =881a(9) =2048a(10) =4761a(11) =11068a(12) =25730a(13) =59815a(14) =139053a(15) =323259a(16) =751486a(17) =1746993a(18) =4061266a(19) =9441298a(20) =21948355a(21) =51023735a(22) =118615793a(23) =275748264a(24) =641036941a(25) =1490230088a(26) =3464364646a(27) =8053670703a(28) =18722512905a(29) =43524561955