987
772
132
9876 is the largest four digit number you can make if all the digits must be different.
99,887
The largest 5 digit number having 3 different digit is
The largest 3 digit number whose digits are all primes is 777. The largest 3 digit number with different prime digits is 753.
The largest 4-digit number with two different digits is 9998. Its successor is the next number, which is 9999. However, 9999 has only one digit (9), so we need to find the next valid 4-digit number with two different digits. This number is 10000, which is technically a 5-digit number, so the largest valid number with two different digits before 9999 is 9998, and its successor cannot be a 4-digit number with two different digits. Thus, there is no valid successor that meets the criteria.
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9876543
9876 (:
123
999 is the largest 3-digit number.