21039 has 4 divisors (see below), whose sum is σ = 28056. Its totient is φ = 14024.

The previous prime is 21031. The next prime is 21059. The reversal of 21039 is 93012.

21039 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

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 21039 - 2³ = 21031 is a prime.

It is a D-number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21031) 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, 3504 + ... + 3509.

It is an arithmetic number, because the mean of its divisors is an integer number (7014).

2²¹⁰³⁹ is an apocalyptic number.

21039 is a deficient number, since it is larger than the sum of its proper divisors (7017).

21039 is an equidigital number, since it uses as much as digits as its factorization.

21039 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7016.

The product of its (nonzero) digits is 54, while the sum is 15.

The square root of 21039 is about 145.0482678283. The cubic root of 21039 is about 27.6063102564.

It can be divided in two parts, 2103 and 9, that added together give a palindrome (2112).

The spelling of 21039 in words is "twenty-one thousand, thirty-nine".