The problem is:
a^21 is congruent to a (mod 15)
the author gave a hint: By Fermat's Little Theorem a^5 is congruent to a (mod 5)
We think we figured out the cases where 3 and 5 do not divide a and where
both 3 and 5 do divide a. It's the other two cases where we have not figured out
what to do. Any insights or help would be apprecited.
TIA
AL Rachels
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