How many positive integer solutions does the above congruency have?
Bonus Problem : Looking ahead, what about or even ?
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Relevant wiki: Chinese Remainder Theorem
Since 2 0 1 6 = 7 × 9 × 3 2 , we can solve the congruence x 3 ≡ 1 modulo 7, 9, and 32 and then multiply the numbers of solutions, by the Chinese Remainder Theorem.
While there is a general theory, the numbers are so small that we can easily do this "by inspection".
Modulo 7 we find the solutions x ≡ 1 , 2 , 4 , and modulo 9 we have x ≡ 1 , 4 , 7 .
Note that x 8 ≡ 1 ( m o d 3 2 ) for odd x . Thus, if x 3 ≡ 1 ( m o d 3 2 ) , then x 9 ≡ x ≡ 1 ( m o d 3 2 ) , so that x ≡ 1 is the only solution in this case.
The total number of solutions is 3 × 3 × 1 = 9