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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