OFFSET
1,2
COMMENTS
a(n) is also number of ways to place n nonattacking pieces rook + leaper[6,6] on an n X n chessboard.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..24
Vaclav Kotesovec, Non-attacking chess pieces, Sixth edition, p. 633, Feb 02 2013.
Vaclav Kotesovec, Mathematica program for this sequence
Roberto Tauraso, The Dinner Table Problem: The Rectangular Case, INTEGERS: Electronic Journal of Combinatorial Number Theory, Vol. 6 (2006), #A11.
FORMULA
Asymptotic (R. Tauraso 2006, quadratic term V. Kotesovec 2011): a(n)/n! ~ (1 + 20/n + 168/n^2)/e^2.
Generally (for this sequence is d=6): 1/e^2*(1+4(d-1)/n+2d*(3d-4)/n^2+...).
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Vaclav Kotesovec, Apr 19 2011
EXTENSIONS
Terms a(23)-a(24) from Vaclav Kotesovec, Apr 21 2012
STATUS
approved