21724128 has 36 divisors (see below), whose sum is σ = 61778808. Its totient is φ = 7241280.

The previous prime is 21724111. The next prime is 21724133. The reversal of 21724128 is 82142712.

It is a tau number, because it is divible by the number of its divisors (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 37428 + ... + 38003.

It is an arithmetic number, because the mean of its divisors is an integer number (1716078).

Almost surely, 2^21724128 is an apocalyptic number.

It is an amenable number.

21724128 is an abundant number, since it is smaller than the sum of its proper divisors (40054680).

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

21724128 is a wasteful number, since it uses less digits than its factorization.

21724128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75447 (or 75436 counting only the distinct ones).

The product of its digits is 1792, while the sum is 27.

The square root of 21724128 is about 4660.9149316416. The cubic root of 21724128 is about 279.0277846457.

The spelling of 21724128 in words is "twenty-one million, seven hundred twenty-four thousand, one hundred twenty-eight".