21204224 has 36 divisors (see below), whose sum is σ = 42758436. Its totient is φ = 10493952.

The previous prime is 21204223. The next prime is 21204241. The reversal of 21204224 is 42240212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 10445824 + 10758400 = 3232^2 + 3280^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21204223) 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, 28562 + ... + 29294.

Almost surely, 2^21204224 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 21204224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21379218).

21204224 is an abundant number, since it is smaller than the sum of its proper divisors (21554212).

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

21204224 is an equidigital number, since it uses as much as digits as its factorization.

21204224 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 862 (or 848 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 17.

The square root of 21204224 is about 4604.8044475309. The cubic root of 21204224 is about 276.7838809151.

Adding to 21204224 its reverse (42240212), we get a palindrome (63444436).

The spelling of 21204224 in words is "twenty-one million, two hundred four thousand, two hundred twenty-four".