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A360702
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Number of sets of 2n words of length 2n over binary alphabet where each letter occurs 2n^2 times.
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2
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1, 2, 394, 10247250, 41192135957378, 26708408307353573010350, 3044454667114388718324075325130428, 65233919825974729088553743803268484284650384722, 275236371094876077407367002758415347571615535684540339803854604
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OFFSET
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0,2
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COMMENTS
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Also the number of inequivalent 2n X 2n {0,1} matrices with distinct rows and equal numbers of 0's and 1's, modulo permutation of the rows. a(1) = 2: [00/11], [01/10].
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LINKS
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FORMULA
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EXAMPLE
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a(0) = 1: {}.
a(1) = 2: {aa,bb}, {ab,ba}.
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MAPLE
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g:= proc(n, i, j) option remember; expand(`if`(j=0, 1, `if`(i<0, 0, add(
g(n, i-1, j-k)*x^(i*k)*binomial(binomial(n, i), k), k=0..j))))
end:
a:= n-> coeff(g(2*n$3), x, 2*n^2):
seq(a(n), n=0..10);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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