This number is a prime.
Théorie des Nombres by Adrien-Marie Legendre contained 859 large quarto pages and was the first text to record the observation that there seemed to be a curious connection between the prime counting function and the logarithm function.
The largest 3-digit distinct-digit prime p such that replacing any of its digits with the digit 3, the result is always a prime, i.e., 359, 839, 853. Note that a concatenation of these three primes, i.e., 359853839 is also prime. [Loungrides]
The sum of the first 859 beast numbers is divisible by the beast. [Gaydos]