login
A189564
Number of permutations p of 1,2,...,n satisfying |p(i+1)-p(i)|<>5 and |p(j+5)-p(j)|<>1 for all i=1..n-1, j=1..n-5.
7
1, 1, 2, 6, 24, 120, 336, 1474, 8340, 57756, 475658, 4171070, 41950294, 472535256, 5882635676, 79963449714, 1173614446044
OFFSET
0,3
COMMENTS
a(n) is also the number of ways to place n nonattacking pieces rook + leaper[1,5] 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