21805207 has 8 divisors (see below), whose sum is σ = 22296384. Its totient is φ = 21317088.

The previous prime is 21805181. The next prime is 21805213. The reversal of 21805207 is 70250812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21805207 - 2⁷ = 21805079 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 (21805297) 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 7 ways as a sum of consecutive naturals, for example, 19218 + ... + 20320.

It is an arithmetic number, because the mean of its divisors is an integer number (2787048).

Almost surely, 2^21805207 is an apocalyptic number.

21805207 is a deficient number, since it is larger than the sum of its proper divisors (491177).

21805207 is a wasteful number, since it uses less digits than its factorization.

21805207 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1529.

The product of its (nonzero) digits is 1120, while the sum is 25.

The square root of 21805207 is about 4669.6045871144. The cubic root of 21805207 is about 279.3744837477.

The spelling of 21805207 in words is "twenty-one million, eight hundred five thousand, two hundred seven".