21728823 has 8 divisors (see below), whose sum is σ = 29238000. Its totient is φ = 14352768.

The previous prime is 21728809. The next prime is 21728827. The reversal of 21728823 is 32882712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21728823 - 2⁴ = 21728807 is a prime.

It is a super-3 number, since 3×21728823³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728827) 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, 32898 + ... + 33551.

It is an arithmetic number, because the mean of its divisors is an integer number (3654750).

Almost surely, 2^21728823 is an apocalyptic number.

21728823 is a deficient number, since it is larger than the sum of its proper divisors (7509177).

21728823 is a wasteful number, since it uses less digits than its factorization.

21728823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66561.

The product of its digits is 10752, while the sum is 33.

The square root of 21728823 is about 4661.4185609104. The cubic root of 21728823 is about 279.0478842800.

The spelling of 21728823 in words is "twenty-one million, seven hundred twenty-eight thousand, eight hundred twenty-three".