Number of isoscent sequences of length n with exactly one descent.

Terms

a(0) =1a(1) =6a(2) =29a(3) =124a(4) =499a(5) =1933a(6) =7307a(7) =27166a(8) =99841a(9) =363980a(10) =1319404a(11) =4763927a(12) =17155264a(13) =61672791a(14) =221499015a(15) =795198010a(16) =2854898575a(17) =10253237150a(18) =36846414395a(19) =132518215788a(20) =477049025009