A189565 - OEIS

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A189565

Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)|<>3 and |p(j+3)-p(j)|<>2 for all i=1..n-2, j=1..n-3.

1, 1, 2, 6, 12, 36, 174, 708, 4334, 31424, 263732, 2503296, 26844578, 316692056, 4090634212, 57274447458, 863488976620

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

COMMENTS

a(n) is also the number of ways to place n nonattacking pieces rook + leaper[2,3] on an n X n chessboard (in fairy chess the leaper [2,3] is called a zebra).

LINKS

Table of n, a(n) for n=0..16.

V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)

FORMULA

Asymptotic: a(n)/n! ~ 1/e^4.

CROSSREFS

Cf. A137774, A189358, A189563, A189564.

Sequence in context: A121404 A202337 A189854 * A074442 A162589 A225957

Adjacent sequences: A189562 A189563 A189564 * A189566 A189567 A189568

KEYWORD

nonn,more,hard

AUTHOR

Vaclav Kotesovec, Apr 23 2011

STATUS

approved