IMO 1978 LL CZS11

Find all natural numbers n < 1978 with the following property:

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IMO 1978 LL CZS11

Origin: CZS

Problem

Find all natural numbers n < 1978 with the following property: If m is a natural number, 1 < m < n, and (m, n) = 1 (i.e., m and n are relatively prime), then m is a prime number.