21265185820 has 12 divisors (see below), whose sum is σ = 44656890264. Its totient is φ = 8506074320.

The previous prime is 21265185817. The next prime is 21265185841. The reversal of 21265185820 is 2858156212.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 531629626 + ... + 531629665.

It is an arithmetic number, because the mean of its divisors is an integer number (3721407522).

Almost surely, 2^21265185820 is an apocalyptic number.

21265185820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21265185820 is an abundant number, since it is smaller than the sum of its proper divisors (23391704444).

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

21265185820 is a wasteful number, since it uses less digits than its factorization.

21265185820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1063259300 (or 1063259298 counting only the distinct ones).

The product of its (nonzero) digits is 76800, while the sum is 40.

The spelling of 21265185820 in words is "twenty-one billion, two hundred sixty-five million, one hundred eighty-five thousand, eight hundred twenty".