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A212139
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Triangular array: T(n,k) is the number of k-element subsets of {1,...,n} that satisfy mean=median.
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4
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1, 2, 1, 3, 3, 1, 4, 6, 2, 1, 5, 10, 4, 3, 1, 6, 15, 6, 7, 2, 1, 7, 21, 9, 13, 5, 3, 1, 8, 28, 12, 22, 10, 8, 2, 1, 9, 36, 16, 34, 18, 18, 6, 3, 1, 10, 45, 20, 50, 30, 36, 14, 9, 2, 1, 11, 55, 25, 70, 48, 66, 32, 23, 7, 3, 1, 12, 66, 30, 95, 72, 114, 64, 55, 20, 10, 2, 1
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OFFSET
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1,2
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COMMENTS
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LINKS
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EXAMPLE
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First 7 rows:
1
2...1
3...3....1
4...6....2...1
5...10...4...3....1
6...15...6...7....2...1
7...21...9...13...5...3...1
T(5,3) counts these subsets: {1,2,3}, 1,3,5}, {2,3,4}, {3,4,5}.
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MATHEMATICA
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t[n_, k_] := t[n, k] = Count[Map[Median[#] == Mean[#] &, Subsets[Range[n], {k}]], True]
Flatten[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]
TableForm[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]
s[n_] := Sum[t[n, k], {k, 1, n}]
Table[s[n], {n, 1, 22}] (* A212146 *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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