I think its more then 20
987,653
The greatest 4-digit number with no repeated digits is... 9876
94205 if digits are not to be repeated and 99999 if digits can be repeated
763920
987,654
98,764
987,653
The greatest 4-digit number with no repeated digits is... 9876
98,764
94205 if digits are not to be repeated and 99999 if digits can be repeated
763920
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
987,654
987653
98,764
9876543.
98,764