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A189850
Number of ways to place n nonattacking composite pieces rook + rider[1,3] on an n X n chessboard.
5
1, 2, 6, 8, 24, 126, 316, 1344, 7782, 33930, 172430, 1106754, 6432236, 45188572, 372437930, 2728674526, 23648822368, 233010291526, 2083328647344
OFFSET
1,2
COMMENTS
In fairy chess, the rider [1,3] is called a Camelrider.
a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+k)-p(i)|<>3k AND |p(j+3k)-p(j)|<>k for all i>=1, j>=1, k>=1, i+k<=n, j+3k<=n
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 29 2011
STATUS
approved