21939 has 8 divisors (see below), whose sum is σ = 29952. Its totient is φ = 14280.

The previous prime is 21937. The next prime is 21943. The reversal of 21939 is 93912.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21939 - 2¹ = 21937 is a prime.

It is a plaindrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (21937) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 162 + ... + 264.

It is an arithmetic number, because the mean of its divisors is an integer number (3744).

2²¹⁹³⁹ is an apocalyptic number.

21939 is a deficient number, since it is larger than the sum of its proper divisors (8013).

21939 is a wasteful number, since it uses less digits than its factorization.

21939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 177.

The product of its digits is 486, while the sum is 24.

The square root of 21939 is about 148.1181960463. The cubic root of 21939 is about 27.9944716977.

The spelling of 21939 in words is "twenty-one thousand, nine hundred thirty-nine".