21228928 has 128 divisors (see below), whose sum is σ = 53856000. Its totient is φ = 8128512.

The previous prime is 21228901. The next prime is 21228953. The reversal of 21228928 is 82982212.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is a junction number, because it is equal to n+sod(n) for n = 21228893 and 21228902.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 493675 + ... + 493717.

It is an arithmetic number, because the mean of its divisors is an integer number (420750).

Almost surely, 2^21228928 is an apocalyptic number.

21228928 is a gapful number since it is divisible by the number (28) 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 21228928, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26928000).

21228928 is an abundant number, since it is smaller than the sum of its proper divisors (32627072).

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

21228928 is a wasteful number, since it uses less digits than its factorization.

21228928 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 112 (or 100 counting only the distinct ones).

The product of its digits is 9216, while the sum is 34.

The square root of 21228928 is about 4607.4860824532. The cubic root of 21228928 is about 276.8913283007.

The spelling of 21228928 in words is "twenty-one million, two hundred twenty-eight thousand, nine hundred twenty-eight".