Number of permutations p of [n] such that p(i) > p(i+1) iff i == 0 (mod 9).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =1a(8) =1a(9) =1a(10) =9a(11) =54a(12) =219a(13) =714a(14) =2001a(15) =5004a(16) =11439a(17) =24309a(18) =48619a(19) =831384a(20) =9069651a(21) =64369341a(22) =355150566a(23) =1635163542a(24) =6542615421a(25) =23369110326a(26) =75953123676a(27) =227864057851