This number is a composite.

+ Concatenate the first two prime factors of 138 to get the third. [Cramer]

+ 138 is the only three-digit number m such that π(m) and prime(m) are palindromic numbers. [Firoozbakht]

+ Arithmetic mean of the first eighteen emirps. [Bajpai]

(There are 6 curios for this number that have not yet been approved by an editor.)

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