21058 has 4 divisors (see below), whose sum is σ = 31590. Its totient is φ = 10528.

The previous prime is 21031. The next prime is 21059. The reversal of 21058 is 85012.

It is a happy number.

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

It can be written as a sum of positive squares in only one way, i.e., 15129 + 5929 = 123^2 + 77^2 .

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21059) by changing a digit.

21058 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5263 + ... + 5266.

2²¹⁰⁵⁸ is an apocalyptic number.

21058 is a deficient number, since it is larger than the sum of its proper divisors (10532).

21058 is a wasteful number, since it uses less digits than its factorization.

21058 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10531.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21058 is about 145.1137484872. The cubic root of 21058 is about 27.6146180353.

It can be divided in two parts, 2 and 1058, that multiplied together give a square (2116 = 46²).

The spelling of 21058 in words is "twenty-one thousand, fifty-eight".