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A212138
Triangular array: T(n,k) is the number of k-element subsets S of {1,...,n} whose average is in S.
3
1, 2, 0, 3, 0, 1, 4, 0, 2, 0, 5, 0, 4, 0, 1, 6, 0, 6, 2, 2, 0, 7, 0, 9, 4, 5, 0, 1, 8, 0, 12, 8, 10, 2, 2, 0, 9, 0, 16, 14, 18, 8, 6, 0, 1, 10, 0, 20, 22, 32, 20, 14, 4, 2, 0, 11, 0, 25, 32, 52, 42, 34, 14, 7, 0, 1, 12, 0, 30, 46, 80, 80, 72, 42, 22, 4, 2, 0, 13, 0, 36, 62, 119, 1
OFFSET
1,2
EXAMPLE
First 7 rows:
1
2...0
3...0...1
4...0...2...0
5...0...4...0...1
6...0...6...2...2...0
7...0...9...4...5...0...1
T(5,3) counts these subsets: {1,2,3}, {1,3,5}, {2,3,4}, {3,4,5}.
MATHEMATICA
t[n_, k_] := Length[Flatten[Map[Apply[Intersection, #] &,
Select[Map[{#, {Mean[#]}} &, Subsets[Range[n], {k}]], IntegerQ[Last[Last[#]]] &]]]]
Flatten[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]
TableForm[Table[t[n, k], {n, 1, 12}, {k, 1, n}]]
(* Peter J. C. Moses, May 01 2012 *)
CROSSREFS
Cf. A061865.
Sequence in context: A361755 A362755 A035614 * A133735 A238801 A095704
KEYWORD
nonn,tabl,changed
AUTHOR
Clark Kimberling, May 06 2012
STATUS
approved