21255257856 has 144 divisors (see below), whose sum is σ = 65065785344. Its totient is φ = 6034010112.

The previous prime is 21255257741. The next prime is 21255257869. The reversal of 21255257856 is 65875255212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 831441 + ... + 856623.

Almost surely, 2^21255257856 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21255257856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32532892672).

21255257856 is an abundant number, since it is smaller than the sum of its proper divisors (43810527488).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21255257856 is a wasteful number, since it uses less digits than its factorization.

21255257856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25366 (or 25352 counting only the distinct ones).

The product of its digits is 1680000, while the sum is 48.

The spelling of 21255257856 in words is "twenty-one billion, two hundred fifty-five million, two hundred fifty-seven thousand, eight hundred fifty-six".