21715021 has 4 divisors (see below), whose sum is σ = 21959100. Its totient is φ = 21470944.

The previous prime is 21715007. The next prime is 21715049. The reversal of 21715021 is 12051712.

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 7502121 + 14212900 = 2739^2 + 3770^2 .

It is a cyclic number.

It is not a de Polignac number, because 21715021 - 2⁵ = 21714989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21715021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21715061) 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, 121906 + ... + 122083.

It is an arithmetic number, because the mean of its divisors is an integer number (5489775).

Almost surely, 2^21715021 is an apocalyptic number.

It is an amenable number.

21715021 is a deficient number, since it is larger than the sum of its proper divisors (244079).

21715021 is an equidigital number, since it uses as much as digits as its factorization.

21715021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 244078.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21715021 is about 4659.9378751224. The cubic root of 21715021 is about 278.9887886623.

Adding to 21715021 its reverse (12051712), we get a palindrome (33766733).

The spelling of 21715021 in words is "twenty-one million, seven hundred fifteen thousand, twenty-one".