21564877821 has 8 divisors (see below), whose sum is σ = 28758413664. Its totient is φ = 14373963600.

The previous prime is 21564877813. The next prime is 21564877837. The reversal of 21564877821 is 12877846512.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21564877821 - 2³ = 21564877813 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21564877121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 636130 + ... + 669171.

It is an arithmetic number, because the mean of its divisors is an integer number (3594801708).

Almost surely, 2^21564877821 is an apocalyptic number.

It is an amenable number.

21564877821 is a deficient number, since it is larger than the sum of its proper divisors (7193535843).

21564877821 is a wasteful number, since it uses less digits than its factorization.

21564877821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1310811.

The product of its digits is 1505280, while the sum is 51.

The spelling of 21564877821 in words is "twenty-one billion, five hundred sixty-four million, eight hundred seventy-seven thousand, eight hundred twenty-one".