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National and Regional Contests
PEN Problems
PEN O Problems
24
24
Part of
PEN O Problems
Problems
(1)
O 24
Source:
5/25/2007
Find the number of subsets of
{
1
,
2
,
⋯
,
2000
}
\{1, 2, \cdots, 2000 \}
{
1
,
2
,
⋯
,
2000
}
, the sum of whose elements is divisible by
5
5
5
.