A187490 - OEIS

%I #11 Mar 09 2018 12:15:38

%S 1,2,6,12,22,31,49,70,99,128,176,216,284,343,423,515,633,722,860,1007,

%T 1173,1333,1552,1729,1989,2223,2502,2809,3138,3416,3819,4226,4658,

%U 5049,5570,6016,6601,7146,7719,8371,9100,9686,10461,11208,12039

%N Number of 3-element nondividing subsets of {1, 2, ..., n}.

%C A set is called nondividing if no element divides the sum of any nonempty subset of the other elements.

%H Alois P. Heinz, <a href="/A187490/b187490.txt">Table of n, a(n) for n = 7..200</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/NondividingSet.html">Nondividing Set.</a>

%e a(7) = 1 because there is one 3-element nondividing subset of {1,2,3,4,5,6,7}: {4,6,7}.

%e a(9) = 6: {4,6,7}, {4,6,9}, {5,6,8}, {5,8,9}, {6,7,9}, {6,8,9}.

%Y Column 3 of triangle A187489. Cf. A068063.

%K nonn

%O 7,2

%A _Alois P. Heinz_, Mar 10 2011