Key Concepts
A factor of n divides n with no remainder. A multiple of n equals n × k for integer k.
A prime has exactly 2 factors: 1 and itself. 1 is NOT prime.
LCM = least common multiple; GCF = greatest common factor.
Even numbers are divisible by 2. Odd numbers are not.
Must-Memorize Primes
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47
Quick Formula
LCM(a,b) = (a × b) ÷ GCF(a,b)
Example
Find the LCM of 12 and 18.
GCF(12,18) = 6 → LCM = (12×18)÷6 = 36