A weighted tribonacci sequence, (1,3,9).

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =37a(5) =121a(6) =376a(7) =1072a(8) =3289a(9) =9889a(10) =29404a(11) =88672a(12) =265885a(13) =796537a(14) =2392240a(15) =7174816a(16) =21520369a(17) =64574977a(18) =193709428a(19) =581117680a(20) =1743420757a(21) =5230158649a(22) =15690480040a(23) =47071742800a(24) =141214610761a(25) =423644159521