21715521 has 4 divisors (see below), whose sum is σ = 28954032. Its totient is φ = 14477012.

The previous prime is 21715489. The next prime is 21715541. The reversal of 21715521 is 12551712.

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 21715521 - 2⁵ = 21715489 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21715491 and 21715500.

It is not an unprimeable number, because it can be changed into a prime (21715541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3619251 + ... + 3619256.

It is an arithmetic number, because the mean of its divisors is an integer number (7238508).

Almost surely, 2^21715521 is an apocalyptic number.

It is an amenable number.

21715521 is a deficient number, since it is larger than the sum of its proper divisors (7238511).

21715521 is an equidigital number, since it uses as much as digits as its factorization.

21715521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7238510.

The product of its digits is 700, while the sum is 24.

The square root of 21715521 is about 4659.9915235974. The cubic root of 21715521 is about 278.9909299347.

The spelling of 21715521 in words is "twenty-one million, seven hundred fifteen thousand, five hundred twenty-one".