21255257857 has 4 divisors (see below), whose sum is σ = 21283561216. Its totient is φ = 21226954500.

The previous prime is 21255257741. The next prime is 21255257869. The reversal of 21255257857 is 75875255212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21255257857 - 2⁷ = 21255257729 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21255257857.

It is not an unprimeable number, because it can be changed into a prime (21255254857) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14150553 + ... + 14152054.

It is an arithmetic number, because the mean of its divisors is an integer number (5320890304).

Almost surely, 2^21255257857 is an apocalyptic number.

It is an amenable number.

21255257857 is a deficient number, since it is larger than the sum of its proper divisors (28303359).

21255257857 is an equidigital number, since it uses as much as digits as its factorization.

21255257857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28303358.

The product of its digits is 1960000, while the sum is 49.

The spelling of 21255257857 in words is "twenty-one billion, two hundred fifty-five million, two hundred fifty-seven thousand, eight hundred fifty-seven".