21728959 has 4 divisors (see below), whose sum is σ = 24833104. Its totient is φ = 18624816.

The previous prime is 21728947. The next prime is 21728963. The reversal of 21728959 is 95982712.

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

It is not a de Polignac number, because 21728959 - 2⁷ = 21728831 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 (21728909) 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, 1552062 + ... + 1552075.

It is an arithmetic number, because the mean of its divisors is an integer number (6208276).

Almost surely, 2^21728959 is an apocalyptic number.

21728959 is a deficient number, since it is larger than the sum of its proper divisors (3104145).

21728959 is an equidigital number, since it uses as much as digits as its factorization.

21728959 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3104144.

The product of its digits is 90720, while the sum is 43.

The square root of 21728959 is about 4661.4331487215. The cubic root of 21728959 is about 279.0484664627.

The spelling of 21728959 in words is "twenty-one million, seven hundred twenty-eight thousand, nine hundred fifty-nine".