Question 214394
There are several combinations that could fit that.
2 200-digit primes, a 100 and a 300 digit #, etc.
------------
In some cases, 2 200-digit #s will give a 399 digit product.
EG, 23*29 = 667 (3 digits)
31*43 = 1333 (4 digits)
-------------------
If the product of the 2 MS digits is more than 10, the result will be 400 digits.