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63973 = 7 x 13 x 19 x 37, is the first Carmichael number to have 4 prime factors with entirely odd digits (totalling 7 digits, with 7 being one of those factors). The sum of those prime factors is 76 = 2^2 x 19, hence the mean of the prime factors is 19, which is one of those factors. Exactly half of the first 12 Carmichael numbers have entirely odd digits in each of their 3 prime factors. [Carmichael]


  Submitted: 2004-11-06 10:03:04;   Last Modified: 2008-01-30 11:28:00.

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