21604320 has 120 divisors (see below), whose sum is σ = 76290984. Its totient is φ = 5757696.

The previous prime is 21604313. The next prime is 21604321. The reversal of 21604320 is 2340612.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21604293 and 21604302.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21604321) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 12127 + ... + 13793.

Almost surely, 2^21604320 is an apocalyptic number.

21604320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21604320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38145492).

21604320 is an abundant number, since it is smaller than the sum of its proper divisors (54686664).

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

21604320 is a wasteful number, since it uses less digits than its factorization.

21604320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1694 (or 1677 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21604320 is about 4648.0447502149. The cubic root of 21604320 is about 278.5138951345.

Adding to 21604320 its reverse (2340612), we get a palindrome (23944932).

The spelling of 21604320 in words is "twenty-one million, six hundred four thousand, three hundred twenty".