Number of permutations p of [n] such that p(i) > p(i+1) iff i == 0 (mod 6).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =6a(8) =27a(9) =83a(10) =209a(11) =461a(12) =923a(13) =10284a(14) =80991a(15) =414961a(16) =1671853a(17) =5699149a(18) =17116009a(19) =278723178a(20) =3135810159a(21) =22493048843a(22) =124606826189a(23) =574688719793