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A189567
Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)|<>5 and |p(j+5)-p(j)|<>2 for all i=1..n-2, j=1..n-5.
4
1, 1, 2, 6, 24, 120, 392, 1810, 10400, 72228, 589674, 5196870, 52398658, 588036216, 7274466172, 98024173852, 1427556373892
OFFSET
0,3
COMMENTS
a(n) is also the number of ways to place n nonattacking pieces rook + leaper[2,5] on an n X n chessboard.
FORMULA
Asymptotic: a(n)/n! ~ 1/e^4.
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Vaclav Kotesovec, Apr 23 2011
STATUS
approved