A divisibility rule is a heuristic for determining whether a positive integer can be evenly divided by another (i.e. there is no remainder left over).

For example determining if a number is even is as simple as checking to see if its last digit is 2, 4, 6, 8 or 0.

Multiple divisibility rules applied to the same number in this way can help quickly determine its prime factorization without having to guess at its prime factors.

Divisibliity Rules applies with numbers 2, 3, 5, 7, 11, 13, 17, 19,........ which are prime numbers.

So, divisibility rules are endless.