Mock AIME 3 Pre 2005 Problems/Problem 12

Revision as of 18:18, 25 April 2009 by God of Math (talk | contribs) (Solution)

Problem

Determine the number of integers $n$ such that $1 \le n \le 1000$ and $n^{12} - 1$ is divisible by $73$.

Solution

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We see a pattern when we look at the numbers that do fulfull this property. The first number is $1$. Then $3, 8, 9, 24, 27, ....$. This follows a pattern. The first number being $1$, and the rest being the previous $+2, +5, +1, +15, +3, +19, +3, +15, +1, +5, +2$. This sequence then repeats itself. We hence find that there are a total of $11*15 - 1$ or $\boxed{164}$ numbers that satisfy the inequality.

See also

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