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 A134646 Number of n X n (0,1,2)-matrices with every row sum 3 and column sum 3. 3
 0, 2, 31, 1344, 111920, 16214000, 3758757240, 1310799454720, 655551508577280, 452647176631372800, 418399785559398720000, 504669505260741099417600, 777461035821119354357452800, 1501959201213688265322501427200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES Zhonghua Tan, Shanzhen Gao, Kenneth Mathies, Joshua Fallon, Counting (0,1,2)-Matrices, Congressus Numeratium, December 2008. LINKS R. H. Hardin, Table of n, a(n) for n=1..99 FORMULA a(n) = 6^{-n} Sum_{alpha = 0 .. n} Sum_{beta = 0 .. n-alpha } \frac{(-4)^{(n-alpha -beta )}3^{beta }(n!)^{2}(beta +3alpha )!}{(alpha !)^{2}beta !(n-alpha -beta )!6^{alpha }} EXAMPLE a(2) = 2: 21 12 12 21 CROSSREFS Cf. A000681, A134645. Sequence in context: A246970 A246969 A358567 * A197320 A239332 A350940 Adjacent sequences: A134643 A134644 A134645 * A134647 A134648 A134649 KEYWORD nonn,easy AUTHOR Shanzhen Gao, Nov 05 2007 EXTENSIONS Definition corrected and a(7) and a(8) found (by direct enumeration) by R. H. Hardin, Oct 18 2009 a(9) - a(99) from R. H. Hardin Feb 06 2010 STATUS approved

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Last modified December 3 09:03 EST 2022. Contains 358515 sequences. (Running on oeis4.)