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Number theory Difficulty 3.5 AMC 10/12 Find the answer

Suppose that nn is the product of three consecutive integers and that nn is divisible by 77. Which of the following is not necessarily a divisor of nn?

Pick one

Solution

Solution 1
Whenever nn is the product of three consecutive integers, nn is divisible by 3!3!, meaning it is divisible by 66.
It also mentions that it is divisible by 77, so the number is definitely divisible by all the factors of 4242.
In our answer choices, the one that is not a factor of 4242 is (D) 28\boxed{\textbf{(D)}\ 28}.

Solution 2
We can look for counterexamples. For example, letting n=131415n = 13 \cdot 14 \cdot 15, we see that nn is not divisible by 28, so (D) 28\boxed{\textbf{(D) }28} is our answer.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.