Number of descent sequences of length n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =23a(6) =67a(7) =222a(8) =832a(9) =3501a(10) =16412a(11) =85062a(12) =484013a(13) =3004342a(14) =20226212a(15) =146930527a(16) =1146389206a(17) =9566847302a(18) =85073695846a(19) =803417121866