21728549 has 4 divisors (see below), whose sum is σ = 21972780. Its totient is φ = 21484320.

The previous prime is 21728527. The next prime is 21728563. The reversal of 21728549 is 94582712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7059649 + 14668900 = 2657^2 + 3830^2 .

It is a cyclic number.

It is not a de Polignac number, because 21728549 - 2⁸ = 21728293 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728149) 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, 121982 + ... + 122159.

It is an arithmetic number, because the mean of its divisors is an integer number (5493195).

Almost surely, 2^21728549 is an apocalyptic number.

It is an amenable number.

21728549 is a deficient number, since it is larger than the sum of its proper divisors (244231).

21728549 is an equidigital number, since it uses as much as digits as its factorization.

21728549 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 244230.

The product of its digits is 40320, while the sum is 38.

The square root of 21728549 is about 4661.3891706229. The cubic root of 21728549 is about 279.0467113458.

The spelling of 21728549 in words is "twenty-one million, seven hundred twenty-eight thousand, five hundred forty-nine".