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A338614
Number of permutations p of [n] such that |p(i) - p(i-1)| <= 3 and |p(i) - p(i-2)| <= 4.
2
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
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
KEYWORD
nonn,more
AUTHOR
Alois P. Heinz, Nov 03 2020
STATUS
approved