21809217 has 8 divisors (see below), whose sum is σ = 29115424. Its totient is φ = 14521248.

The previous prime is 21809197. The next prime is 21809219. The reversal of 21809217 is 71290812.

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

It is not a de Polignac number, because 21809217 - 2⁶ = 21809153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21809219) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1468 + ... + 6765.

It is an arithmetic number, because the mean of its divisors is an integer number (3639428).

Almost surely, 2^21809217 is an apocalyptic number.

It is an amenable number.

21809217 is a deficient number, since it is larger than the sum of its proper divisors (7306207).

21809217 is an equidigital number, since it uses as much as digits as its factorization.

21809217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9119.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21809217 is about 4670.0339399195. The cubic root of 21809217 is about 279.3916084496.

The spelling of 21809217 in words is "twenty-one million, eight hundred nine thousand, two hundred seventeen".