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A320436
Irregular triangle read by rows where T(n,k) is the number of pairwise coprime k-subsets of {1,...,n}, 1 <= k <= A036234(n), where a single number is not considered to be pairwise coprime unless it is equal to 1.
6
1, 1, 1, 1, 3, 1, 1, 5, 2, 1, 9, 7, 2, 1, 11, 8, 2, 1, 17, 19, 10, 2, 1, 21, 25, 14, 3, 1, 27, 37, 24, 6, 1, 31, 42, 26, 6, 1, 41, 73, 68, 32, 6, 1, 45, 79, 72, 33, 6, 1, 57, 124, 151, 105, 39, 6, 1, 63, 138, 167, 114, 41, 6, 1, 71, 159, 192, 128, 44, 6, 1, 79
OFFSET
1,5
EXAMPLE
Triangle begins:
1
1 1
1 3 1
1 5 2
1 9 7 2
1 11 8 2
1 17 19 10 2
1 21 25 14 3
1 27 37 24 6
1 31 42 26 6
1 41 73 68 32 6
1 45 79 72 33 6
1 57 124 151 105 39 6
1 63 138 167 114 41 6
1 71 159 192 128 44 6
1 79 183 228 157 56 8
MATHEMATICA
Table[Length[Select[Subsets[Range[n], {k}], CoprimeQ@@#&]], {n, 16}, {k, PrimePi[n]+1}]
CROSSREFS
Except for the k = 1 column, same as A186974.
Row sums are A320426.
Second column is A015614.
Sequence in context: A348641 A014475 A358612 * A135228 A021325 A174609
KEYWORD
nonn,tabf
AUTHOR
Gus Wiseman, Jan 08 2019
STATUS
approved