Number of permutations p of [n] such that p(i), p(i+2), p(i+4),... form an up-down sequence for i in {1,2}.
A361648
Number of permutations p of [n] such that p(i), p(i+2), p(i+4),... form an up-down sequence for i in {1,2}.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =3a(4) =6a(5) =20a(6) =80a(7) =350a(8) =1750a(9) =10080a(10) =64512a(11) =450912a(12) =3438204a(13) =28471872a(14) =253913088a(15) =2424193200a(16) =24687555750a(17) =267199961600
External references
- oeis: A361648