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 A172668 Number of 3*n X n 0..2 arrays with row sums 2 and column sums 6. 1
 1, 141, 352128, 6152037276, 467046072593100, 115428185943399529200, 76497104228450459248094400, 118274738663434470504494036529600, 384184227197088213207839624049360408000, 2415977451999318332950627138384873223959560000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS R. H. Hardin, Table of n, a(n) for n = 1..33 FORMULA a(n) = 720^(-n)*n!(3n)! Sum_{i=0..n} Sum_{j=0..n-i} Sum_{k=0..n-i-j} (15^(n-i-k)*45^k*(6i+4j+2k)!/(i!j!k!(n-i-j-k)!(2j+k+3i)!*2^(2j+k+3i))). - Shanzhen Gao, Feb 24 2010 PROG (PARI) a(n) = 720^(-n)*n!*(3*n)!*sum(i=0, n, sum(j=0, n-i, sum(k=0, n-i-j, (15^(n-i-k)*45^k*(6*i+4*j+2*k)!/(i!*j!*k!*(n-i-j-k)!*(2*j+k+3*i)!*2^(2*j+k+3*i)))))) \\ Michel Marcus, Jan 17 2018 CROSSREFS Sequence in context: A164525 A153358 A066627 * A172764 A172836 A087001 Adjacent sequences:  A172665 A172666 A172667 * A172669 A172670 A172671 KEYWORD nonn AUTHOR R. H. Hardin, Feb 06 2010 STATUS approved

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Last modified October 22 18:44 EDT 2019. Contains 328319 sequences. (Running on oeis4.)