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Just showing those entries submitted by 'Carmichael': (Click here to show all) 340561 = 13 x 17 x 23 x 67 is the 2nd 4Brilliant Carmichael Number (the first being 75361), and the first Carmichael Number that truncates to another Carmichael Number (to the first, 561). Its reversal is semiprime. Its digital sum (19) is prime. The sum of prime factors is 120 = 5! = 2^3 x 3 x 5, hence the mean of the prime factors is the primorial 30 = 2 x 3 x 5. [Carmichael]
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