Find the number of integers N lying between 2 and 1 0 0 (inclusive) such that for all integers m such that 3 N ≤ m ≤ 2 N , ( N − 2 m m ) is a multiple of m .
Details and assumptions
N = 2 is considered a solution, since the only integer m such that 3 2 ≤ m ≤ 2 2 is 1 , and ( 2 − 2 ⋅ 1 2 ) is a multiple of 1 .
This problem is not original.
@Calvin sir: The intended expression is ( N − 2 m m ) . This is valid since m ≥ N − 2 m ≥ 0 from the condition 3 N ≤ m ≤ 2 N . Roger Lu has commented why ( N − 2 m N ) doesn't work. Please correct me if I am wrong.
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I do not understand the answer. I do not see any integer > 3 would work. For even number N=2k, (k>1), you can choose m=k and obviously it does not work. For odd number N=2k+1 you can choose m=k, and since ( N N − 2 m ) = 2k+1, which is relatively prime to m=k, that does not work either. Am I missing something?
Yeah, but how do you prove it? This is literally the eighth time I'm seeing a solution which doesn't show how to approach the problem. - _ _ _ _ _ _ _ _ _ _ _ __ -
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Wait the 8th time from me or on this problem because I don't see any other solutions... :O
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Eighth time on Brilliant.
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I have a one word solution that I think will be easily understood:
PRIMES
Any questions?