Number of isoscent sequences of length n with exactly two ascents.

Terms

a(0) =3a(1) =25a(2) =128a(3) =525a(4) =1901a(5) =6371a(6) =20291a(7) =62407a(8) =187272a(9) =552104a(10) =1606762a(11) =4631643a(12) =13256644a(13) =37742047a(14) =107025452a(15) =302585780a(16) =853556449a(17) =2403702976a(18) =6760469822a(19) =18995826302a(20) =53336990264a(21) =149680752886a(22) =419883986837