Is there an answer?

Recently, on one of my math competitions, there was a problem that no one got, in clouding the teacher. So I was wondering if it's even answerable.

A number n has 4 distinct prime factors. Find the number of positive integers that divide n with remainder.

The answer is not:

N-16.

194

Note by Trevor Arashiro
4 years, 11 months ago

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Doesn't this depend on the multiplicity of the distinct prime factors?

Are we looking at n=p1a1p2a2p3a3p4a4n = p_{1}^{a_{1}} * p_{2}^{a_{2}} * p_{3}^{a_{3}} * p_{4}^{a_{4}} for distinct primes pkp_{k} with exponents ak1a_{k} \ge 1?

If so, then the I think the desired number is k=14(ak+1)\prod_{k=1}^4 (a_{k} + 1).

Brian Charlesworth - 4 years, 11 months ago

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Sorry, but I just realized I worded the question slightly wrong. Its supposed to be "with remainder". So for this case, its just nk=14(ak+1)n-\prod_{k=1}^4(a_k+1)

But that's what I was thinking as well. Unfortunately, it's supposedly not the answer

Trevor Arashiro - 4 years, 11 months ago

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Weird. Is there any chance that the source of the supposed answer is incorrect? I see now how the "n - 16" and "194" answers arose; you are looking at 2357=2102*3*5*7 = 210. This number definitely has 1616 divisors, and thus there would be 21016=194210 - 16 = 194 positive integers less than 210210 that would divide into 210210 with non-zero remainder.

Brian Charlesworth - 4 years, 11 months ago

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Do you know what the answer is supposed to be? That could offer a way to backtrack and figure out what they mean.

Calvin Lin Staff - 4 years, 11 months ago

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@Calvin Lin Unfortunately not.

Trevor Arashiro - 4 years, 11 months ago

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What kind of answer is expected? Is it multiple choice, integer answer, short algebraic answer, or long proof form?

Also, what does N-16 and 194 refer to?

Calvin Lin Staff - 4 years, 11 months ago

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Answers that we tried but weren't excepted

Trevor Arashiro - 4 years, 11 months ago

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If it is "with remainder" is the answer infinity?

A Former Brilliant Member - 4 years, 11 months ago

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That's a thought, but the 'standard' interpretation of "positive integer mm divides nn with remainder" assumes that mnm \le n. Since it is stated that nn has 44 distinct prime factors I think that we can assume that this standard interpretation is being applied, otherwise this prime information would have been largely irrelevant.

Brian Charlesworth - 4 years, 11 months ago

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I wasn't aware that I re-shared this. If I did, I certainly didn't intend to.

Gremlins?

Guiseppi Butel - 4 years, 11 months ago

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Haha Actually, there have been some gremlins lurking on Brilliant the past few days. Strange things have been happening when posting/editing solutions, causing format changes, symbols appearing out of nowhere, etc.. So yes, your unintended re-share could have been the work of gremlins. :)

Brian Charlesworth - 4 years, 11 months ago

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