21238558921 has 4 divisors (see below), whose sum is σ = 21256069252. Its totient is φ = 21221048592.

The previous prime is 21238558909. The next prime is 21238558997. The reversal of 21238558921 is 12985583212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5563518921 + 15675040000 = 74589^2 + 125200^2 .

It is a cyclic number.

It is not a de Polignac number, because 21238558921 - 2⁵ = 21238558889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21238552921) 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, 8753346 + ... + 8755771.

It is an arithmetic number, because the mean of its divisors is an integer number (5314017313).

Almost surely, 2^21238558921 is an apocalyptic number.

It is an amenable number.

21238558921 is a deficient number, since it is larger than the sum of its proper divisors (17510331).

21238558921 is a wasteful number, since it uses less digits than its factorization.

21238558921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17510330.

The product of its digits is 345600, while the sum is 46.

The spelling of 21238558921 in words is "twenty-one billion, two hundred thirty-eight million, five hundred fifty-eight thousand, nine hundred twenty-one".