As of August 2017, the largest known prime number is 2^74,207,281 − 1, a number with 22,338,618digits.I attached a link with the 100 largest known prime numbers, there you can see the number of digits.
999998
999,983
99 is the largest two digit number. If I can use the digits anyway I want, then 9 to the 9th power is larger
I suspect that it is 6^940 which is 731 digits long. The largest through reordering the digits is only 9640.
As a string, the largest number is 7111111.
986541
9650 is the largest formed by re-ordering the digits.
86420
the largest five digit number that can be formed using the digits 7 and 9 is 97,000
99997
Without using exponents or factorials, that's it.
The largest ten digit number with no repeated digits is '9876543210'.
976542
6,543,210
651
You get the largest number if you sort the digits, from largest to smallest.