This number is a composite.
The largest number which can be written with all the
digits from 1 to 5 (without repetition) as a sum of primes
in 2 different ways: 541 + 23 = 564 and 523 + 41 = 564. [van Doorn]
The largest prime factor of F11 (the largest completely factored Fermat number) has 564 digits.
(There is one curio for this number that has not yet been approved by an editor.)
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