login
A189853
Number of ways to place n nonattacking composite pieces rook + rider[1,6] on an n X n chessboard.
4
1, 2, 6, 24, 120, 720, 2640, 13596, 87768, 680274, 6090756, 61678252, 482005340, 4454053680, 46705656280, 549750105234
OFFSET
1,2
COMMENTS
a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+k)-p(i)|<>6k AND |p(j+6k)-p(j)|<>k for all i>=1, j>=1, k>=1, i+k<=n, j+6k<=n
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 29 2011
STATUS
approved