21604 has 12 divisors (see below), whose sum is σ = 41328. Its totient is φ = 9800.

The previous prime is 21601. The next prime is 21611. The reversal of 21604 is 40612.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21601) 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, 202 + ... + 289.

It is an arithmetic number, because the mean of its divisors is an integer number (3444).

2²¹⁶⁰⁴ is an apocalyptic number.

It is an amenable number.

21604 is a deficient number, since it is larger than the sum of its proper divisors (19724).

21604 is a wasteful number, since it uses less digits than its factorization.

21604 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506 (or 504 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21604 is about 146.9829922134. The cubic root of 21604 is about 27.8512520025.

It can be divided in two parts, 21 and 604, that added together give a 4-th power (625 = 5⁴).

The spelling of 21604 in words is "twenty-one thousand, six hundred four".