21604420 has 36 divisors (see below), whose sum is σ = 47178180. Its totient is φ = 8300544.

The previous prime is 21604397. The next prime is 21604421. The reversal of 21604420 is 2440612.

It can be written as a sum of positive squares in 6 ways, for example, as 2262016 + 19342404 = 1504^2 + 4398^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21604421) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 111844 + ... + 112036.

It is an arithmetic number, because the mean of its divisors is an integer number (1310505).

Almost surely, 2^21604420 is an apocalyptic number.

21604420 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 21604420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23589090).

21604420 is an abundant number, since it is smaller than the sum of its proper divisors (25573760).

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

21604420 is a wasteful number, since it uses less digits than its factorization.

21604420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 424 (or 229 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 19.

The square root of 21604420 is about 4648.0555074138. The cubic root of 21604420 is about 278.5143248533.

The spelling of 21604420 in words is "twenty-one million, six hundred four thousand, four hundred twenty".