The product of all digits of positive integer M is 105. How many such Ms are there with four digits?
+876 Prime factor of 105 -> 3*5*7
The number has 3, 5, 7, and 1
These are 4 distinct, so there are 4! ways
this is the only case b/c there is no multiplication of 3,5,7 that is 1 digit
The answer is 4!
