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 A287377 Triangle read by rows: T(n,m) is the number of inequivalent n X m matrices under action of the Klein group, with one-seventh each of 1's, 2's, 3's, 4's, 5's, 6's and 7's (ordered occurrences rounded up/down if n*m != 0 mod 7). 8
 1, 1, 1, 1, 1, 1, 1, 1, 1, 22680, 1, 1, 5040, 3742560, 4540536000, 1, 1, 113400, 851370480, 6518191680000, 54111175679736000 (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..36 of triangle, flattened M. Merino and I. Unanue, Counting squared grid patterns with Pólya Theory, EKAIA, 34 (2018), 289-316 (in Basque). FORMULA g(x1,x2,x3,x4,x5,x6,x7)=(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 coefficient correspond to y1=Sum_{i=1..7} x_i, y2=Sum_{i=1..7} x_i^2, and occurrences of numbers are ceiling(m*n/7) for the first k numbers and floor(m*n/7) for the last (7-k) numbers, if m*n = k mod 7. EXAMPLE For n = 4 and m = 2 the T(4,2) = 5040 solutions are colorings of 4 X 2 matrices in 7 colors inequivalent under the action of the Klein group with exactly 2, 1, 1, 1, 1, 1, 1 occurrences of each color (coefficient of x1^2 x2^1 x3^1 x4^1 x5^1 x6^1 x7^1). Triangle begins: ============================================================== n\m | 0  1  2      3           4             5 ----|--------------------------------------------------------- 0   | 1 1   | 1  1 2   | 1  1  1 3   | 1  1  1       22680 4   | 1  1  5040    3742560    4540536000 5   | 1  1  113400  851370480  6518191680000  54111175679736000 CROSSREFS Cf. A283435, A286892, A287020, A287021, A287022, A287378, A287383, A287384. Sequence in context: A251789 A105378 A279443 * A179726 A287249 A263238 Adjacent sequences:  A287374 A287375 A287376 * A287378 A287379 A287380 KEYWORD nonn,tabl AUTHOR María Merino, Imanol Unanue, May 24 2017 STATUS approved

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Last modified September 24 07:34 EDT 2021. Contains 347623 sequences. (Running on oeis4.)