21437725921 has 4 divisors (see below), whose sum is σ = 21443569344. Its totient is φ = 21431882500.

The previous prime is 21437725913. The next prime is 21437725937. The reversal of 21437725921 is 12952773412.

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 not a de Polignac number, because 21437725921 - 2³ = 21437725913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21437725961) 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, 2916205 + ... + 2923546.

It is an arithmetic number, because the mean of its divisors is an integer number (5360892336).

Almost surely, 2^21437725921 is an apocalyptic number.

It is an amenable number.

21437725921 is a deficient number, since it is larger than the sum of its proper divisors (5843423).

21437725921 is an equidigital number, since it uses as much as digits as its factorization.

21437725921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5843422.

The product of its digits is 211680, while the sum is 43.

The spelling of 21437725921 in words is "twenty-one billion, four hundred thirty-seven million, seven hundred twenty-five thousand, nine hundred twenty-one".