21158538 has 16 divisors (see below), whose sum is σ = 42553056. Its totient is φ = 7013520.

The previous prime is 21158519. The next prime is 21158549. The reversal of 21158538 is 83585112.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21158499 and 21158508.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8656 + ... + 10827.

It is an arithmetic number, because the mean of its divisors is an integer number (2659566).

Almost surely, 2^21158538 is an apocalyptic number.

21158538 is an abundant number, since it is smaller than the sum of its proper divisors (21394518).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21158538 is a wasteful number, since it uses less digits than its factorization.

21158538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19669.

The product of its digits is 9600, while the sum is 33.

The square root of 21158538 is about 4599.8410842115. The cubic root of 21158538 is about 276.5849544985.

The spelling of 21158538 in words is "twenty-one million, one hundred fifty-eight thousand, five hundred thirty-eight".