Factors and Multiples
Prime Check
Decide whether 17 is prime by testing every whole number from 2 up to the square root of 17. If none divide 17 evenly, the number is prime.
Example
prime-check-17.math
prime check: 17
step: 17 ÷ 2 = 8 remainder 1 (not a factor)
step: 17 ÷ 3 = 5 remainder 2 (not a factor)
step: 17 ÷ 4 = 4 remainder 1 (not a factor)
step: 17 is prime
primality-test
A prime number has exactly two factors: 1 and itself. To check, try dividing by 2, 3, 4, … up to the square root. If any trial succeeds (remainder 0), the number is composite. Stop as soon as one works.