OFFSET
0,3
COMMENTS
a(n) is also number of ways to place n nonattacking pieces rook + semi-leaper[6,6] on an n X n chessboard.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..24 (Updated Jan 19 2019)
Vaclav Kotesovec, Non-attacking chess pieces, 6ed, 2013, p. 644.
Vaclav Kotesovec, Mathematica program for this sequence
George Spahn and Doron Zeilberger, Counting Permutations Where The Difference Between Entries Located r Places Apart Can never be s (For any given positive integers r and s), arXiv:2211.02550 [math.CO], 2022.
FORMULA
Asymptotics (V. Kotesovec, Mar 2011): a(n)/n! ~ (1 + 11/n + 30/n^2)/e.
Generally (for this sequence is d=6): 1/e*(1+(2d-1)/n+d*(d-1)/n^2).
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 19 2011
EXTENSIONS
Terms a(23)-a(24) from Vaclav Kotesovec, Apr 21 2012
STATUS
approved