a(n) = n plus sum of previous three terms.

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =15a(5) =30a(6) =58a(7) =110a(8) =206a(9) =383a(10) =709a(11) =1309a(12) =2413a(13) =4444a(14) =8180a(15) =15052a(16) =27692a(17) =50941a(18) =93703a(19) =172355a(20) =317019a(21) =583098a(22) =1072494a(23) =1972634a(24) =3628250a(25) =6673403a(26) =12274313a(27) =22575993a(28) =41523737a(29) =76374072