Divisor 20491

To determine if any number is divisible by 20491, you must apply 2 tests successively. If all of them 'pass' - that is, if your number is divisible by 31 and 661 - then it is divisible by 20491.

The following tests must pass:

• Test if a number is divisible by 31
• Test if a number is divisible by 661

Easy!