21200809 has 16 divisors (see below), whose sum is σ = 24754176. Its totient is φ = 17784000.

The previous prime is 21200801. The next prime is 21200821. The reversal of 21200809 is 90800212.

It is a cyclic number.

It is not a de Polignac number, because 21200809 - 2³ = 21200801 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21200809.

It is not an unprimeable number, because it can be changed into a prime (21200801) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 110904 + ... + 111094.

It is an arithmetic number, because the mean of its divisors is an integer number (1547136).

Almost surely, 2^21200809 is an apocalyptic number.

It is an amenable number.

21200809 is a deficient number, since it is larger than the sum of its proper divisors (3553367).

21200809 is a wasteful number, since it uses less digits than its factorization.

21200809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 456.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21200809 is about 4604.4336242365. The cubic root of 21200809 is about 276.7690211761.

The spelling of 21200809 in words is "twenty-one million, two hundred thousand, eight hundred nine".