divisibility test造句

For a 3-digit number in base 10, this number has a relatively simple divisibility test.
Given the divisibility test for 99 is not a harshad number, since 9 + 9 = 18, and 99 is not divisible by 18.
Digit sums and digital roots can be used for quick divisibility tests : a natural number is divisible by 3 or 9 if and only if its digit sum ( or digital root ) is divisible by 3 or 9, respectively.
It's difficult to find divisibility test in a sentence. 用divisibility test造句挺难的