|
|
A194487
|
|
Number of ways to arrange 3 nonattacking knights on the lower triangle of an n X n board.
|
|
1
|
|
|
0, 1, 12, 62, 253, 804, 2136, 4958, 10376, 20013, 36144, 61846, 101163, 159286, 242748, 359634, 519806, 735143, 1019796, 1390458, 1866649, 2471016, 3229648, 4172406, 5333268, 6750689, 8467976, 10533678, 13001991, 15933178, 19394004
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
|
|
LINKS
|
|
|
FORMULA
|
Empirical: a(n) = (1/48)*n^6 + (1/16)*n^5 - (17/16)*n^4 + (133/48)*n^3 + (433/24)*n^2 - (743/6)*n + 218 for n>4.
Empirical g.f.: x^2*(1 + 5*x - x^2 + 36*x^3 - 50*x^4 + 50*x^5 - 40*x^6 + 22*x^7 - 12*x^8 + 4*x^9) / (1 - x)^7. - Colin Barker, May 05 2018
|
|
EXAMPLE
|
Some solutions for 3 X 3:
..1......0......1......1......0......0......1......0......0......0......1
..0.1....1.1....1.1....1.0....0.1....0.1....0.1....1.0....1.1....0.0....0.0
..1.0.0..1.0.0..0.0.0..1.0.0..0.1.1..1.0.1..0.0.1..1.1.0..0.1.0..1.1.1..1.0.1
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|