Prime Curios!: 90

90
(another Prime Pages' Curiosity)

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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]

Submitted: 2000-11-02 09:09:13; Last Modified: 2009-09-16 11:19:40.