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A287383 Triangle read by rows: T(n,m) is the number of inequivalent n X m matrices under action of the Klein group, with one-ninth each of 1's, 2's, 3's, 4's, 5's, 6's, 7's, 8's and 9's (ordered occurrences rounded up/down if n*m != 0 mod 9). 8
1, 1, 1, 1, 1, 1, 1, 1, 1, 90720, 1, 1, 1, 14968800, 40864824000, 1, 1, 453600, 5108114880, 131993382447360, 3463115239584000000 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,10

COMMENTS

Computed using Polya's enumeration theorem for coloring.

LINKS

María Merino, Rows n=0..34 of triangle, flattened

M. Merino and I. Unanue, Counting squared grid patterns with Pólya Theory, EKAIA, 34 (2018), 289-316 (in Basque).

FORMULA

G.f.: g(x1,x2,x3,x4,x5,x6,x7,x8,x9) = (y1^(m*n) + 3*y2^(m*n/2))/4 for even n and m; (y1^(m*n) + y1^n*y2^((m*n-m)/2) + 2*y2^(m*n/2))/4 for odd n and even m; (y1^(m*n) + y1^m*y2^((m*n-n)/2) + 2*y2^(m*n/2))/4 for even n and odd m; (y1^(m*n) + y1^n*y2^((m*n-n)/2) + y1^m*y2^((m*n-m)/2) + y1*y2^((m*n-1)/2))/4 for odd n and m; where the coefficients y1 and y2 correspond to y1 = Sum_{i=1..9} x_i and y2 = Sum_{i=1..9} x_i^2. Occurrences of numbers are ceiling(m*n/9) for the first k numbers and floor(m*n/9) for the last (9-k) numbers, if m*n = k mod 9.

EXAMPLE

For n = 3 and m = 3 the T(3,3) = 90720 solutions are colorings of 3 X 3 matrices in 9 colors inequivalent under the action of the Klein group with exactly 1 occurrence of each color (coefficient of x1^1, x2^1, x3^1, x4^1, x5^1, x6^1, x7^1, x8^1, x9^1).

Triangle begins:

===================================================================

n\m | 0  1  2       3           4                5

----|--------------------------------------------------------------

0   | 1

1   | 1  1

2   | 1  1  1

3   | 1  1  1       90720

4   | 1  1  1       14968800    40864824000

5   | 1  1  453600  5108114880  131993382447360  3463115239584000000

CROSSREFS

Cf. A283435, A286892, A287020, A287021, A287022, A287377, A287378, A287384.

Sequence in context: A270754 A252915 A075007 * A179732 A131353 A183677

Adjacent sequences:  A287380 A287381 A287382 * A287384 A287385 A287386

KEYWORD

nonn,tabl

AUTHOR

María Merino, Imanol Unanue, May 24 2017

STATUS

approved

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Last modified May 16 21:28 EDT 2021. Contains 343951 sequences. (Running on oeis4.)