Anti Fermat's little theorem

Number Theory Level 2

True or false:

Because $$1729 = 7\times13\times19$$ is not a prime number, we can't apply Fermat's little theorem (FLT) to the following congruence:

$2^{1728} \equiv 1 \pmod {1729}.$

Because we can't apply FLT, the congruence above is incorrect.

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