21579 has 4 divisors (see below), whose sum is σ = 28776. Its totient is φ = 14384.

The previous prime is 21577. The next prime is 21587. The reversal of 21579 is 97512.

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

It is a cyclic number.

It is not a de Polignac number, because 21579 - 2¹ = 21577 is a prime.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (21577) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3594 + ... + 3599.

It is an arithmetic number, because the mean of its divisors is an integer number (7194).

2²¹⁵⁷⁹ is an apocalyptic number.

21579 is a deficient number, since it is larger than the sum of its proper divisors (7197).

21579 is an equidigital number, since it uses as much as digits as its factorization.

21579 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7196.

The product of its digits is 630, while the sum is 24.

The square root of 21579 is about 146.8979237430. The cubic root of 21579 is about 27.8405047636.

The spelling of 21579 in words is "twenty-one thousand, five hundred seventy-nine".