21723213 has 16 divisors (see below), whose sum is σ = 31201280. Its totient is φ = 13399344.

The previous prime is 21723211. The next prime is 21723227. The reversal of 21723213 is 31232712.

It is not a de Polignac number, because 21723213 - 2¹ = 21723211 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21723213.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21723211) 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 15 ways as a sum of consecutive naturals, for example, 1981 + ... + 6882.

It is an arithmetic number, because the mean of its divisors is an integer number (1950080).

Almost surely, 2^21723213 is an apocalyptic number.

It is an amenable number.

21723213 is a deficient number, since it is larger than the sum of its proper divisors (9478067).

21723213 is a wasteful number, since it uses less digits than its factorization.

21723213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8928.

The product of its digits is 504, while the sum is 21.

The square root of 21723213 is about 4660.8167739142. The cubic root of 21723213 is about 279.0238671274.

Adding to 21723213 its reverse (31232712), we get a palindrome (52955925).

The spelling of 21723213 in words is "twenty-one million, seven hundred twenty-three thousand, two hundred thirteen".