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A189837
Number of ways to place n nonattacking composite pieces rook + rider[1,2] on an n X n chessboard.
6
1, 2, 2, 8, 12, 22, 58, 276, 648, 2304, 6508, 24528, 96402, 466922, 2271738, 13723826, 76579326, 512425626, 3281233020, 24654941268, 175398054696
OFFSET
1,2
COMMENTS
(In fairy chess the rider [1,2] is called a Nightrider, Rook + Nightrider = Waran.)
a(n) is also the number of permutations p of 1,2,...,n satisfying |p(i+k) - p(i)| <> 2k AND |p(j+2k) - p(j)| <> k for all i >= 1, j >= 1, k >= 1, i+k <= n, j+2k <= n.
CROSSREFS
Sequence in context: A008828 A254219 A053414 * A274409 A302118 A014236
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 29 2011
STATUS
approved