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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. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..72.

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.

Cf. A051424, A084422, A085945, A187106, A276187, A320423, A320430, A320435.

Sequence in context: A245369 A076334 A014475 * A135228 A021325 A174609

Adjacent sequences:  A320433 A320434 A320435 * A320437 A320438 A320439

KEYWORD

nonn,tabf

AUTHOR

Gus Wiseman, Jan 08 2019

STATUS

approved

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Last modified April 5 03:15 EDT 2020. Contains 333238 sequences. (Running on oeis4.)