

A189563


Number of permutations p of 1,2,...,n satisfying p(i+1)p(i)<>4 and p(j+4)p(j)<>1 for all i=1..n1, j=1..n4.


8



1, 2, 6, 24, 48, 182, 868, 5752, 37156, 296944, 2738820, 28894206, 335399468, 4285522402, 59536763892, 892785282788
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OFFSET

1,2


COMMENTS

a(n) is also the number of ways to place n nonattacking pieces rook + leaper[1,4] on an n X n chessboard (in fairy chess the leaper[1,4] is called a giraffe).


LINKS

Table of n, a(n) for n=1..16.
V. Kotesovec, Number of ways of placing nonattacking queens, kings, bishops and knights (in English and Czech)


FORMULA

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


CROSSREFS

Cf. A137774, A189358.
Sequence in context: A113904 A099144 A189851 * A104114 A175624 A118038
Adjacent sequences: A189560 A189561 A189562 * A189564 A189565 A189566


KEYWORD

nonn,hard


AUTHOR

Vaclav Kotesovec, Apr 23 2011


STATUS

approved



