cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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.

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%I A320436 #7 Jan 08 2019 19:06:58
%S A320436 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,
%T A320436 24,6,1,31,42,26,6,1,41,73,68,32,6,1,45,79,72,33,6,1,57,124,151,105,
%U A320436 39,6,1,63,138,167,114,41,6,1,71,159,192,128,44,6,1,79
%N 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.
%e A320436 Triangle begins:
%e A320436    1
%e A320436    1   1
%e A320436    1   3   1
%e A320436    1   5   2
%e A320436    1   9   7   2
%e A320436    1  11   8   2
%e A320436    1  17  19  10   2
%e A320436    1  21  25  14   3
%e A320436    1  27  37  24   6
%e A320436    1  31  42  26   6
%e A320436    1  41  73  68  32   6
%e A320436    1  45  79  72  33   6
%e A320436    1  57 124 151 105  39   6
%e A320436    1  63 138 167 114  41   6
%e A320436    1  71 159 192 128  44   6
%e A320436    1  79 183 228 157  56   8
%t A320436 Table[Length[Select[Subsets[Range[n],{k}],CoprimeQ@@#&]],{n,16},{k,PrimePi[n]+1}]
%Y A320436 Except for the k = 1 column, same as A186974.
%Y A320436 Row sums are A320426.
%Y A320436 Second column is A015614.
%Y A320436 Cf. A051424, A084422, A085945, A187106, A276187, A320423, A320430, A320435.
%K A320436 nonn,tabf
%O A320436 1,5
%A A320436 _Gus Wiseman_, Jan 08 2019