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A331477
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Number of n element multisets of n element multisets of an n-set.
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2
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1, 1, 6, 220, 73815, 286243776, 13949678575756, 8800321588119330984, 73241437035618231162682185, 8183604949527627465377060678018870, 12477686558866630120430437118910496237274716, 263383624455446425760290611316122951917033704595478840
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = binomial(binomial(2*n - 1, n) + n - 1, n).
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EXAMPLE
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The a(2) = 6 multisets are:
{{1,1}, {1,1}},
{{1,1}, {1,2}},
{{1,1}, {2,2}},
{{1,2}, {1,2}},
{{1,2}, {2,2}},
{{2,2}, {2,2}}.
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MATHEMATICA
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Table[Binomial[Binomial[2n-1, n]+n-1, n], {n, 0, 20}] (* Harvey P. Dale, Aug 19 2021 *)
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PROG
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(PARI) a(n)={binomial(binomial(2*n - 1, n) + n - 1, n)}
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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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