 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/ii/paper-2/15c/a/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

The order of

a

N

r

such that

a^{r} \equiv 1 (mod N) .

It exists because

a

is a unit in the finite group

(Z / N Z)^{\times}

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