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90 (another Prime Pages' Curiosity) |
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There are only 7 positive integers n for which the number of primes < n (pi(n)) equals the number of positive integers < n relative prime to n (phi(n)). They are 2, 3, 4, 8, 14, 20 and 90. [Moser] (903 - 1)/(90 - 1) is a Mersenne prime. [Goormaghtigh]
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