611114.
98756 999,998
The largest prime number that has 4 digits and begins with a 1 is 1,999.
As a string, the largest number is 7111111.
4312
If the digits are only used once, each, the largest possible number would be 97,531
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.
To form the largest even number, the last digit must be even, which means it can be either 8, 4, or 2. Placing the largest even digit, 8, in the ones place, we can continue selecting the next largest digits in descending order until all digits are used.
987654312
4312
As of January 25, 2014, the largest known prime number was calculated to be 257,885,161 − 1; a number containing 17,425,170 digits. This is, of course, too large to display.
As of October 2015, the largest known prime number is 2^57,885,161 − 1, a number with 17,425,170 digits.
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