so in https://web2.0calc.com/questions/let-m-be-the-least-common-multiple-of-1-2-3-20-how_1 why do you only multiply the red numbers?
what do the red numbers mean?
The least common multiple includes the numbers with the most factors of 2, 3, 5, 7, 11, 13, and so on. The red numbers are just the numbers with the most factors of a specific prime. In other words, if you wanted to find the lcm of 1,2,3, and 4, then you would prime factor each number:
There is a number with 2 2s in its prime factorization, so 2^2 x 3 is our lcm.
Same with all the numbers from 1-20. Find the prime factors of each number and then find the number with the most 2s, 3s, and so on (I'm just listing the primes).