21445728 has 48 divisors (see below), whose sum is σ = 56770560. Its totient is φ = 7088256.

The previous prime is 21445727. The next prime is 21445751. The reversal of 21445728 is 82754412.

It is a tau number, because it is divible by the number of its divisors (48).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21445727) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 11313 + ... + 13071.

It is an arithmetic number, because the mean of its divisors is an integer number (1182720).

Almost surely, 2^21445728 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 21445728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28385280).

21445728 is an abundant number, since it is smaller than the sum of its proper divisors (35324832).

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

21445728 is a wasteful number, since it uses less digits than its factorization.

21445728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1899 (or 1891 counting only the distinct ones).

The product of its digits is 17920, while the sum is 33.

The square root of 21445728 is about 4630.9532496021. The cubic root of 21445728 is about 277.8307200542.

The spelling of 21445728 in words is "twenty-one million, four hundred forty-five thousand, seven hundred twenty-eight".