123456789

This number is a composite.

+ Relocating a single digit converts it into a concatenation of five primes: 234156789 _ 23 : 41 : 5 : 67 : 89. [Trigg]

+ (123456789)111 x 102285 + 1 is prime. Note 123456789 is repeated 111 times. [Dubner]

+ Replacing each of the digits, one-by-one with a 0, yields primes in three cases: 1, 2, and 7 (023456789, 103456789, and 123456089). Note that 127 is a Mersenne prime. [Trotter]

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

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