Doubt - MXMLCM

Find prime factorization of each number.

20 75 72 13

=>
(2^2 * 5^1) , (3^1*5^2), (2^3*3^2), (13^1)
Find max power of 2, max power of 3, max power of 5 and so on for each prime number.
=> LCM = 2^3 * 3^2 * 5^2 * 13^1

please see this it will clear your doubt