21173 has 4 divisors (see below), whose sum is σ = 21888. Its totient is φ = 20460.

The previous prime is 21169. The next prime is 21179. The reversal of 21173 is 37112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21173 - 2² = 21169 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 (21179) 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, 311 + ... + 372.

It is an arithmetic number, because the mean of its divisors is an integer number (5472).

2²¹¹⁷³ is an apocalyptic number.

It is an amenable number.

21173 is a deficient number, since it is larger than the sum of its proper divisors (715).

21173 is an equidigital number, since it uses as much as digits as its factorization.

21173 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 714.

The product of its digits is 42, while the sum is 14.

The square root of 21173 is about 145.5094498649. The cubic root of 21173 is about 27.6647956026.

Adding to 21173 its reverse (37112), we get a palindrome (58285).

It can be divided in two parts, 2 and 1173, that multiplied together give a triangular number (2346 = T₆₈).

The spelling of 21173 in words is "twenty-one thousand, one hundred seventy-three", and thus it is an iban number.