# 399

This number is a composite.

The smallest Lucas-Carmichael number.

399 = 7^{1} + 7^{2} + 7^{3} [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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