21228173 has 4 divisors (see below), whose sum is σ = 21237660. Its totient is φ = 21218688.

The previous prime is 21228167. The next prime is 21228209. The reversal of 21228173 is 37182212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 779689 + 20448484 = 883^2 + 4522^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21228173 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21228133) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 683 + ... + 6551.

It is an arithmetic number, because the mean of its divisors is an integer number (5309415).

Almost surely, 2^21228173 is an apocalyptic number.

It is an amenable number.

21228173 is a deficient number, since it is larger than the sum of its proper divisors (9487).

21228173 is an equidigital number, since it uses as much as digits as its factorization.

21228173 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9486.

The product of its digits is 1344, while the sum is 26.

The square root of 21228173 is about 4607.4041498440. The cubic root of 21228173 is about 276.8880457448. Note that the first 3 decimals are identical.

The spelling of 21228173 in words is "twenty-one million, two hundred twenty-eight thousand, one hundred seventy-three".