643

This number is a prime.

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As Alois P. Heinz discovered, 643 is the smallest nonprime among integers a(n) greater than 1 so that multiplying the n-th highly composite number by a(n) will give a highly composite number. a(643) = 6 is not prime. [Post]

Submitted: 2013-10-25 17:35:06; Last Modified: 2018-12-23 01:30:02.