Number of compositions of n with exactly three descents.

Terms

a(0) =3a(1) =18a(2) =78a(3) =264a(4) =786a(5) =2097a(6) =5179a(7) =11998a(8) =26400a(9) =55593a(10) =112814a(11) =221639a(12) =423318a(13) =788518a(14) =1436302a(15) =2564135a(16) =4494967a(17) =7750068a(18) =13160903a(19) =22039386a(20) =36434095a(21) =59514365a(22) =96139570a(23) =153699716a(24) =243345157a(25) =381779187a(26) =593848668a(27) =916277405a(28) =1403004758a(29) =2132797015