55555

This number is a composite.

+ The larger of two repdigit numbers consisting of d identical digits d whose the concatenation in order of all prime factors is prime, i.e., 55555 = 5*41*271 and 541271 is prime. (The other is 22 for which, 22 = 2*11 and 211 is prime). [Loungrides]

(There is one curio for this number that has not yet been approved by an editor.)

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