21604513 has 4 divisors (see below), whose sum is σ = 24690880. Its totient is φ = 18518148.

The previous prime is 21604487. The next prime is 21604523. The reversal of 21604513 is 31540612.

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 21604513 - 2⁵ = 21604481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21604523) 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, 1543173 + ... + 1543186.

It is an arithmetic number, because the mean of its divisors is an integer number (6172720).

Almost surely, 2^21604513 is an apocalyptic number.

It is an amenable number.

21604513 is a deficient number, since it is larger than the sum of its proper divisors (3086367).

21604513 is an equidigital number, since it uses as much as digits as its factorization.

21604513 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3086366.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21604513 is about 4648.0655115865. The cubic root of 21604513 is about 278.5147244906.

The spelling of 21604513 in words is "twenty-one million, six hundred four thousand, five hundred thirteen".