what is the gcd of 2001 and 6837?

Question

how do you find this one?

Answer 1

Factors for 2001 are 1, 3, 23, 29, 69, 87, 667 and 2001

Factors for 6837 which has any of the above is only 3, so GCD is 3. 

Answer 2

2001 = 1*3*23*29
6837 = 1*3*43*53
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              GCD
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If sum of all digits in the number is divisible by 3 or 9 that whole number is dividable by 3 or 9:
2+0+0+1=3
6+8+3+7=24