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A189568
Number of permutations p of 1,2,...,n satisfying |p(i+3)-p(i)|<>4 and |p(j+4)-p(j)|<>3 for all i=1..n-3, j=1..n-4.
3
1, 1, 2, 6, 24, 80, 326, 1566, 9544, 65036, 518498, 4750006, 48830634, 554929274, 6926227324, 93970452970, 1377573324202
OFFSET
0,3
COMMENTS
a(n) is also the number of ways to place n nonattacking pieces rook + leaper[3,4] 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