21959 has 4 divisors (see below), whose sum is σ = 25104. Its totient is φ = 18816.

The previous prime is 21943. The next prime is 21961. The reversal of 21959 is 95912.

It is a happy number.

21959 is an esthetic number in base 7, because in such base its adjacent digits differ by 1.

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

It is not a de Polignac number, because 21959 - 2⁴ = 21943 is a prime.

It is a Duffinian number.

It is a plaindrome in base 15.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21959.

It is not an unprimeable number, because it can be changed into a prime (21929) 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, 1562 + ... + 1575.

It is an arithmetic number, because the mean of its divisors is an integer number (6276).

2²¹⁹⁵⁹ is an apocalyptic number.

21959 is a deficient number, since it is larger than the sum of its proper divisors (3145).

21959 is an equidigital number, since it uses as much as digits as its factorization.

21959 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3144.

The product of its digits is 810, while the sum is 26.

The square root of 21959 is about 148.1856943163. The cubic root of 21959 is about 28.0029758742.

It can be divided in two parts, 219 and 59, that multiplied together give a palindrome (12921).

The spelling of 21959 in words is "twenty-one thousand, nine hundred fifty-nine".