21904521 has 4 divisors (see below), whose sum is σ = 29206032. Its totient is φ = 14603012.

The previous prime is 21904489. The next prime is 21904523. The reversal of 21904521 is 12540912.

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 21904521 - 2⁵ = 21904489 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21904491 and 21904500.

It is not an unprimeable number, because it can be changed into a prime (21904523) 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, 3650751 + ... + 3650756.

It is an arithmetic number, because the mean of its divisors is an integer number (7301508).

Almost surely, 2^21904521 is an apocalyptic number.

It is an amenable number.

21904521 is a deficient number, since it is larger than the sum of its proper divisors (7301511).

21904521 is an equidigital number, since it uses as much as digits as its factorization.

21904521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7301510.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 21904521 is about 4680.2265970784. The cubic root of 21904521 is about 279.7979877923.

The spelling of 21904521 in words is "twenty-one million, nine hundred four thousand, five hundred twenty-one".