21239 has 4 divisors (see below), whose sum is σ = 21624. Its totient is φ = 20856.

The previous prime is 21227. The next prime is 21247. The reversal of 21239 is 93212.

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 21239 - 2⁸ = 20983 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 (21269) 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, 92 + ... + 225.

It is an arithmetic number, because the mean of its divisors is an integer number (5406).

2²¹²³⁹ is an apocalyptic number.

21239 is a deficient number, since it is larger than the sum of its proper divisors (385).

21239 is an equidigital number, since it uses as much as digits as its factorization.

21239 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 384.

The product of its digits is 108, while the sum is 17.

The square root of 21239 is about 145.7360627985. The cubic root of 21239 is about 27.6935111459.

The spelling of 21239 in words is "twenty-one thousand, two hundred thirty-nine".