564

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.