21105173 has 4 divisors (see below), whose sum is σ = 21123948. Its totient is φ = 21086400.

The previous prime is 21105169. The next prime is 21105179. The reversal of 21105173 is 37150112.

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 5121169 + 15984004 = 2263^2 + 3998^2 .

It is a cyclic number.

It is not a de Polignac number, because 21105173 - 2² = 21105169 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 (21105179) 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, 7586 + ... + 9987.

It is an arithmetic number, because the mean of its divisors is an integer number (5280987).

Almost surely, 2^21105173 is an apocalyptic number.

It is an amenable number.

21105173 is a deficient number, since it is larger than the sum of its proper divisors (18775).

21105173 is a wasteful number, since it uses less digits than its factorization.

21105173 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18774.

The product of its (nonzero) digits is 210, while the sum is 20.

The square root of 21105173 is about 4594.0366781296. The cubic root of 21105173 is about 276.3522291805.

Adding to 21105173 its reverse (37150112), we get a palindrome (58255285).

The spelling of 21105173 in words is "twenty-one million, one hundred five thousand, one hundred seventy-three".