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+ There are only 8 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, 10, 14, 20, and 90. [Moser]

+ (903 - 1)/(90 - 1) is a Mersenne prime. [Goormaghtigh]

(There is one curio for this number that has not yet been approved by an editor.)

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