Number of permutations of length n such that numbers at odd positions are monotone and numbers at even positions are also monotone.
A257546
Number of permutations of length n such that numbers at odd positions are monotone and numbers at even positions are also monotone.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =24a(5) =40a(6) =80a(7) =140a(8) =280a(9) =504a(10) =1008a(11) =1848a(12) =3696a(13) =6864a(14) =13728a(15) =25740a(16) =51480a(17) =97240a(18) =194480a(19) =369512a(20) =739024a(21) =1410864a(22) =2821728a(23) =5408312a(24) =10816624a(25) =20801200a(26) =41602400a(27) =80233200a(28) =160466400a(29) =310235040
External references
- oeis: A257546