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International Contests
Baltic Way
2003 Baltic Way
7
7
Part of
2003 Baltic Way
Problems
(1)
Maximise the cardinality of X
Source: Baltic Way 2003
11/6/2010
A subset of
X
X
X
of
{
1
,
2
,
3
,
…
10000
}
\{1,2,3, \ldots 10000 \}
{
1
,
2
,
3
,
…
10000
}
has the following property: If
a
,
b
a,b
a
,
b
are distinct elements of
X
X
X
, then
a
b
∉
X
ab\not\in X
ab
∈
X
. What is the maximal number of elements in
X
X
X
?
combinatorics unsolved
combinatorics