399
This number is a composite.
The smallest Lucas-Carmichael number.
399 = 71 + 72 + 73 [Capelle]
The smallest number, all of whose prime factors are of form
4n+3, whose sum of distinct prime factors is prime: 3*7*19
= 399; 3+7+19 = 29. [Post]
(There is one curio for this number that has not yet been approved by an editor.)
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