Divisor 21979

To determine if any number is divisible by 21979, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 31 and 709 - then it is divisible by 21979.

The following tests must pass:

• Test if a number is divisible by 31
• Test if a number is divisible by 709

Easy!