21028224 has 64 divisors (see below), whose sum is σ = 63843840. Its totient is φ = 6007296.

The previous prime is 21028213. The next prime is 21028229. The reversal of 21028224 is 42282012.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a self number, because there is not a number n which added to its sum of digits gives 21028224.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21028229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1224 + ... + 6599.

It is an arithmetic number, because the mean of its divisors is an integer number (997560).

Almost surely, 2^21028224 is an apocalyptic number.

21028224 is a gapful number since it is divisible by the number (24) 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 21028224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31921920).

21028224 is an abundant number, since it is smaller than the sum of its proper divisors (42815616).

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

21028224 is an equidigital number, since it uses as much as digits as its factorization.

21028224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7847 (or 7835 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 21028224 is about 4585.6541518087. The cubic root of 21028224 is about 276.0159621098.

The spelling of 21028224 in words is "twenty-one million, twenty-eight thousand, two hundred twenty-four".