How many 3 digit numbers N are there such that the digits of N and 3N are all even? (There is no restriction on the number of digits of 3N)
There are precisely 24 three-digit numbers N such that all the digits of each of N and 3N is even.
Very very hard! I don't know whether I will ever be able to posit an independent semi-analytic explanation of my own together with the number list!!
Puzzle Answer
