A338614 Number of permutations p of [n] such that |p(i) - p(i-1)| <= 3 and |p(i) - p(i-2)| <= 4.

1, 1, 2, 6, 24, 72, 124, 210, 394, 810, 1652, 3168, 5816, 10640, 19794, 37292, 70298, 131618, 245146, 456430, 851670, 1592008, 2976326, 5559808, 10379010, 19374184, 36175422, 67562524, 126185322, 235650426, 440038528

Offset

0,3

Links

Table of n, a(n) for n=0..30.

Wikipedia, Permutation

Maple

b:= proc(s, x, y) option remember; `if`(s={}, 1, add(
      `if`((x=0 or abs(x-j)<=4) and (y=0 or abs(y-j)<=3),
          b(s minus {j}, y, j), 0), j=s))
    end:
a:= n-> b({$1..n}, 0$2):
seq(a(n), n=0..20);

Crossrefs

Cf. A263690, A263696, A263745, A333833, A338738.

Sequence in context: A027562 A236625 A096259 * A087645 A174700 A216158

Adjacent sequences: A338611 A338612 A338613 * A338615 A338616 A338617

Keyword

nonn,more

Author

Alois P. Heinz, Nov 03 2020

Status

approved