21722809 has 4 divisors (see below), whose sum is σ = 21749904. Its totient is φ = 21695716.

The previous prime is 21722801. The next prime is 21722837. The reversal of 21722809 is 90822712.

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 21722809 - 2³ = 21722801 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21722801) 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, 12307 + ... + 13960.

It is an arithmetic number, because the mean of its divisors is an integer number (5437476).

Almost surely, 2^21722809 is an apocalyptic number.

It is an amenable number.

21722809 is a deficient number, since it is larger than the sum of its proper divisors (27095).

21722809 is an equidigital number, since it uses as much as digits as its factorization.

21722809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27094.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21722809 is about 4660.7734336696. The cubic root of 21722809 is about 279.0221373903.

The spelling of 21722809 in words is "twenty-one million, seven hundred twenty-two thousand, eight hundred nine".