21958 has 4 divisors (see below), whose sum is σ = 32940. Its totient is φ = 10978.

The previous prime is 21943. The next prime is 21961. The reversal of 21958 is 85912.

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

It is a plaindrome in base 15.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5488 + ... + 5491.

It is an arithmetic number, because the mean of its divisors is an integer number (8235).

2²¹⁹⁵⁸ is an apocalyptic number.

21958 is a deficient number, since it is larger than the sum of its proper divisors (10982).

21958 is a wasteful number, since it uses less digits than its factorization.

21958 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10981.

The product of its digits is 720, while the sum is 25.

The square root of 21958 is about 148.1823201330. The cubic root of 21958 is about 28.0025507880.

It can be divided in two parts, 21 and 958, that added together give a palindrome (979).

The spelling of 21958 in words is "twenty-one thousand, nine hundred fifty-eight".