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 are 2 curios for this number that have not yet been approved by an editor.)
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