21158173 has 4 divisors (see below), whose sum is σ = 21674268. Its totient is φ = 20642080.

The previous prime is 21158161. The next prime is 21158177. The reversal of 21158173 is 37185112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 12236004 + 8922169 = 3498^2 + 2987^2 .

It is a cyclic number.

It is not a de Polignac number, because 21158173 - 2⁵ = 21158141 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21158177) 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, 257986 + ... + 258067.

It is an arithmetic number, because the mean of its divisors is an integer number (5418567).

Almost surely, 2^21158173 is an apocalyptic number.

It is an amenable number.

21158173 is a deficient number, since it is larger than the sum of its proper divisors (516095).

21158173 is an equidigital number, since it uses as much as digits as its factorization.

21158173 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 516094.

The product of its digits is 1680, while the sum is 28.

The square root of 21158173 is about 4599.8014087567. The cubic root of 21158173 is about 276.5833640595.

The spelling of 21158173 in words is "twenty-one million, one hundred fifty-eight thousand, one hundred seventy-three".