21573823 has 4 divisors (see below), whose sum is σ = 21716848. Its totient is φ = 21430800.

The previous prime is 21573803. The next prime is 21573829. The reversal of 21573823 is 32837512.

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

It is a cyclic number.

It is not a de Polignac number, because 21573823 - 2⁵ = 21573791 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 (21573829) 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, 71286 + ... + 71587.

It is an arithmetic number, because the mean of its divisors is an integer number (5429212).

Almost surely, 2^21573823 is an apocalyptic number.

21573823 is a deficient number, since it is larger than the sum of its proper divisors (143025).

21573823 is a wasteful number, since it uses less digits than its factorization.

21573823 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 143024.

The product of its digits is 10080, while the sum is 31.

The square root of 21573823 is about 4644.7629648885. The cubic root of 21573823 is about 278.3827818807.

The spelling of 21573823 in words is "twenty-one million, five hundred seventy-three thousand, eight hundred twenty-three".