GCD(a,b) - greatest common divisor of numbers a, b. Examples: GCD(20,30) = 10. 10 is the largest number that divides 20 i 30. GCD(45,60) = 15. 15 is the largest number that divides 45 i 60. LCM(a,b) - least common multiple of numbers a, b. Examples: LCM(20,30) = 60. 60 is the least number that can be divided by 20 and 30. LCM(45,60) = 180. 180 is the least number that can be divided by 45 and 60.