OFFSET
0,2
COMMENTS
Also the number of subsets of {1...n} containing no positive differences of the elements and such that all such differences are distinct.
LINKS
Fausto A. C. Cariboni, Table of n, a(n) for n = 0..99 (terms 0..41 from Gus Wiseman, terms 42..80 from Vaclav Kotesovec)
EXAMPLE
The a(0) = 1 through a(5) = 14 subsets:
{1} {2} {3} {4} {5} {6}
{1,2} {1,3} {1,4} {1,5} {1,6}
{2,3} {2,4} {2,5} {2,6}
{3,4} {3,5} {3,6}
{1,2,4} {4,5} {4,6}
{1,3,4} {1,2,5} {5,6}
{1,4,5} {1,2,6}
{2,3,5} {1,3,6}
{2,4,5} {1,4,6}
{1,5,6}
{2,3,6}
{2,5,6}
{3,4,6}
{3,5,6}
MATHEMATICA
Table[Length[Select[Subsets[Range[n]], MemberQ[#, n]&&UnsameQ@@Abs[Subtract@@@Subsets[#, {2}]]&]], {n, 15}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 17 2019
STATUS
approved