The greatest number formed by rearranging the digits is 97514.
There are, however, much larger even number. For example, 954^71 is a number that is larger than googol squared. And 4^(71^95) is very much larger.
<<>>
97541> 97514 . . .
How about 4 to the power 5 to the power 7 to the power 91.
Or how about 4! to the power 5! to the power 7! to the power 91!.
The greatest 4-digit number with no repeated digits is... 9876
987,654
98,764
985,316
24
It is 999999998.
The greatest 4-digit number with no repeated digits is... 9876
To be an even number then the final digit = 2. The largest single prime digit is 7 (as both 8 and 9 are composite). The greatest even number fulfilling the conditions is 77777772.
88888 888...
8642
98,764
987,654
98,764
985,316
987,654
24
The greatest possible number is 888... (repeating).