IMO Shortlist 2017 problem N4
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Avg: 7,0Call a rational number short if it has finitely many digits in its decimal expansion. For a positive integer , we say that a positive integer
is
tastic if there exists a number
such that
is short, and such that
is not short for any
. Let
be the the set of
tastic numbers. Consider
for
What is the maximum number of elements in
?
Izvor: https://www.imo-official.org/problems/IMO2017SL.pdf