21805789 has 4 divisors (see below), whose sum is σ = 21855456. Its totient is φ = 21756124.

The previous prime is 21805783. The next prime is 21805807. The reversal of 21805789 is 98750812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21805789 - 2⁷ = 21805661 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 (21805783) 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, 24169 + ... + 25054.

It is an arithmetic number, because the mean of its divisors is an integer number (5463864).

Almost surely, 2^21805789 is an apocalyptic number.

It is an amenable number.

21805789 is a deficient number, since it is larger than the sum of its proper divisors (49667).

21805789 is an equidigital number, since it uses as much as digits as its factorization.

21805789 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49666.

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 21805789 is about 4669.6669046089. Note that the first 3 decimals coincide. The cubic root of 21805789 is about 279.3769693085.

The spelling of 21805789 in words is "twenty-one million, eight hundred five thousand, seven hundred eighty-nine".