100

This number is a composite.

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100*2^213 - 1 is prime. Note that 213*2^100 - 1 is also prime. This is the smallest pair of three-digit numbers with such property. [Opao]

100 is the smallest perfect square whose summation of the differences between itself and each of its digits, where each difference is raised to the power of the corresponding digit, is equal to a prime number, i.e., (100-1)^1 + (100-0)^0 + (100-0)^0 is prime. [Opao]