Given that 312 is divisible by 26. It will also be divisible by:
3
4
6
13
If a number is divisible by another number, then it is divisible by each of the factors of that number. Factors of 26 = 1, 2, 13, 26
Therefore, 312 is also divisible by 13
123 + 231 + 312 is divisible by:
52 is divisible by 4. It means that 56 also is divisible by 4.