21728320 has 28 divisors (see below), whose sum is σ = 51741324. Its totient is φ = 8691200.

The previous prime is 21728309. The next prime is 21728323. The reversal of 21728320 is 2382712.

It can be written as a sum of positive squares in 2 ways, for example, as 11943936 + 9784384 = 3456^2 + 3128^2 .

It is not an unprimeable number, because it can be changed into a prime (21728323) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33631 + ... + 34270.

Almost surely, 2^21728320 is an apocalyptic number.

21728320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21728320 is an abundant number, since it is smaller than the sum of its proper divisors (30013004).

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

21728320 is an equidigital number, since it uses as much as digits as its factorization.

21728320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67918 (or 67908 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 21728320 is about 4661.3646070652. The cubic root of 21728320 is about 279.0457310392.

The spelling of 21728320 in words is "twenty-one million, seven hundred twenty-eight thousand, three hundred twenty".