**399**= 3 x 7 x 19.

**399**is 333 in base 11.

**399**is the total number of parts in all partitions of 12.

**399**is the smallest Lucas-Carmichael number.

**399**= 7

^{1}+ 7

^{2}+ 7

^{3}.

**399**is the smallest number, all of whose prime factors are of the form 4

*n*+ 3, whose sum of distinct prime factors is prime (3 + 7 + 19 = 29).

**399**is the sum of 11 consecutive primes:

**399**= 17 + 19 + 23 + 29 + 31 + 37 + 41 + 43 + 47 + 53 + 59.

Source: Number Gossip