21644858821 has 4 divisors (see below), whose sum is σ = 21765780000. Its totient is φ = 21523937644.

The previous prime is 21644858797. The next prime is 21644858849. The reversal of 21644858821 is 12885844612.

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 a de Polignac number, because none of the positive numbers 2^k-21644858821 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644858861) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 60460321 + ... + 60460678.

It is an arithmetic number, because the mean of its divisors is an integer number (5441445000).

Almost surely, 2^21644858821 is an apocalyptic number.

It is an amenable number.

21644858821 is a deficient number, since it is larger than the sum of its proper divisors (120921179).

21644858821 is a wasteful number, since it uses less digits than its factorization.

21644858821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120921178.

The product of its digits is 983040, while the sum is 49.

The spelling of 21644858821 in words is "twenty-one billion, six hundred forty-four million, eight hundred fifty-eight thousand, eight hundred twenty-one".