21928728 has 32 divisors (see below), whose sum is σ = 55065600. Its totient is φ = 7277088.

The previous prime is 21928723. The next prime is 21928733. The reversal of 21928728 is 82782912.

It is an interprime number because it is at equal distance from previous prime (21928723) and next prime (21928733).

It is a super-2 number, since 2×21928728² = 961738223395968, which contains 22 as substring.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21928721) 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, 3825 + ... + 7647.

It is an arithmetic number, because the mean of its divisors is an integer number (1720800).

Almost surely, 2^21928728 is an apocalyptic number.

It is an amenable number.

21928728 is an abundant number, since it is smaller than the sum of its proper divisors (33136872).

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

21928728 is a wasteful number, since it uses less digits than its factorization.

21928728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4071 (or 4067 counting only the distinct ones).

The product of its digits is 32256, while the sum is 39.

The square root of 21928728 is about 4682.8119757257. The cubic root of 21928728 is about 279.9010194361.

The spelling of 21928728 in words is "twenty-one million, nine hundred twenty-eight thousand, seven hundred twenty-eight".