21645823 has 4 divisors (see below), whose sum is σ = 21669768. Its totient is φ = 21621880.

The previous prime is 21645817. The next prime is 21645859. The reversal of 21645823 is 32854612.

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 21645823 - 2⁵ = 21645791 is a prime.

It is a Duffinian number.

It is a plaindrome in base 8.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21645023) 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, 10561 + ... + 12442.

It is an arithmetic number, because the mean of its divisors is an integer number (5417442).

Almost surely, 2^21645823 is an apocalyptic number.

21645823 is a deficient number, since it is larger than the sum of its proper divisors (23945).

21645823 is an equidigital number, since it uses as much as digits as its factorization.

21645823 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23944.

The product of its digits is 11520, while the sum is 31.

The square root of 21645823 is about 4652.5071735571. The cubic root of 21645823 is about 278.6921275153.

The spelling of 21645823 in words is "twenty-one million, six hundred forty-five thousand, eight hundred twenty-three".