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A189569
Number of permutations p of 1,2,...,n satisfying |p(i+3)-p(i)|<>5 and |p(j+5)-p(j)|<>3 for all i=1..n-3, j=1..n-5.
2
1, 1, 2, 6, 24, 120, 464, 2274, 13236, 91760, 740562, 6541984, 65632694, 732880076, 8995905626, 120367234946
OFFSET
0,3
COMMENTS
a(n) is also the number of ways to place n nonattacking pieces rook + leaper[3,5] on an n X n chessboard.
FORMULA
Asymptotic: a(n)/n! ~ 1/e^4.
KEYWORD
nonn,more,hard
AUTHOR
Vaclav Kotesovec, Apr 23 2011
STATUS
approved