21564877820 has 24 divisors (see below), whose sum is σ = 46747091328. Its totient is φ = 8347694400.

The previous prime is 21564877813. The next prime is 21564877837. The reversal of 21564877820 is 2877846512.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17390411 + ... + 17391650.

It is an arithmetic number, because the mean of its divisors is an integer number (1947795472).

Almost surely, 2^21564877820 is an apocalyptic number.

21564877820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21564877820 is an abundant number, since it is smaller than the sum of its proper divisors (25182213508).

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

21564877820 is a wasteful number, since it uses less digits than its factorization.

21564877820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34782101 (or 34782099 counting only the distinct ones).

The product of its (nonzero) digits is 1505280, while the sum is 50.

The spelling of 21564877820 in words is "twenty-one billion, five hundred sixty-four million, eight hundred seventy-seven thousand, eight hundred twenty".