21331604 has 48 divisors (see below), whose sum is σ = 45467520. Its totient is φ = 8553600.

The previous prime is 21331589. The next prime is 21331621. The reversal of 21331604 is 40613312.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 53534 + ... + 53930.

It is an arithmetic number, because the mean of its divisors is an integer number (947240).

Almost surely, 2^21331604 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21331604, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22733760).

21331604 is an abundant number, since it is smaller than the sum of its proper divisors (24135916).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21331604 is a wasteful number, since it uses less digits than its factorization.

21331604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 528 (or 526 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 21331604 is about 4618.6149438982. The cubic root of 21331604 is about 277.3370154580.

Adding to 21331604 its reverse (40613312), we get a palindrome (61944916).

The spelling of 21331604 in words is "twenty-one million, three hundred thirty-one thousand, six hundred four".