If the way to crack the RSA algorithm is knowing the factors of a number. How easy can the factors be obtained by taking the reverse 'long product'?.
For instance, if you have the product of three digit numbers(letters for place value) abc * def = ghijk, why can't the last digit k give possible quotients?(1-digit numbers that when multiplyed give last digit as k) These two numbers give the possible numbers that can be multiplied to be added to give j and so on.
How complicated will this constrained tree grow? How is this method complex?