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A187190
Number of 3-turn rook's tours on an n X n board summed over all starting positions
0
0, 8, 108, 480, 1400, 3240, 6468, 11648, 19440, 30600, 45980, 66528, 93288, 127400, 170100, 222720, 286688, 363528, 454860, 562400, 687960, 833448, 1000868, 1192320, 1410000, 1656200, 1933308, 2243808, 2590280, 2975400
OFFSET
1,2
FORMULA
Empirical: a(n) = 4*n^4 - 10*n^3 + 6*n^2.
Empirical G.f.: 4*x^2*(2+17*x+5*x^2)/(1-x)^5. - Colin Barker, Jan 22 2012
EXAMPLE
Some solutions for 3X3
..0..0..3....0..2..3....1..0..2....0..0..3....0..3..0....0..0..0....3..2..0
..0..1..2....0..1..0....0..0..0....0..0..2....0..2..1....0..2..3....0..0..0
..0..0..0....0..0..0....0..0..3....0..0..1....0..0..0....0..1..0....0..1..0
CROSSREFS
Row 3 of A187189.
Sequence in context: A105261 A187288 A275134 * A099762 A246498 A119936
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 06 2011
STATUS
approved