67
961
23 or 41
9409
Ten.
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 three digit prime number whose digits are all primes is 773.
Smallest is 11 & Largest is 77.
7777
73 satisfies your condition.
How about: 773
61 is prime. You cannot make 61 by multiplying four digits.
23
Two-digit prime numbers whose digits add up to 10 are:193773
992
67
11, 19, 41, 61, and 89