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A048046
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Number of nonempty subsets of {1,2,...,n} in which exactly 4/5 of the elements are <= (n+1)/3.
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1
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 8, 9, 45, 50, 55, 165, 180, 195, 455, 490, 525, 1155, 1240, 1326, 3366, 3645, 3933, 11685, 12750, 13860, 41580, 45375, 49335, 138391, 150524, 163175, 433875, 470665, 509067, 1347255, 1461278, 1580761
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OFFSET
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1,11
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LINKS
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MAPLE
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f:= proc(n) local k, j;
k:= floor((n+1)/3);
add(binomial(k, 4/5*j)*binomial(n-k, 1/5*j), j=5..n, 5)
end proc:
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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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