21799209 has 4 divisors (see below), whose sum is σ = 29065616. Its totient is φ = 14532804.

The previous prime is 21799199. The next prime is 21799241. The reversal of 21799209 is 90299712.

It is a happy number.

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 not a de Polignac number, because 21799209 - 2⁵ = 21799177 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21799279) 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, 3633199 + ... + 3633204.

It is an arithmetic number, because the mean of its divisors is an integer number (7266404).

Almost surely, 2^21799209 is an apocalyptic number.

It is an amenable number.

21799209 is a deficient number, since it is larger than the sum of its proper divisors (7266407).

21799209 is an equidigital number, since it uses as much as digits as its factorization.

21799209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7266406.

The product of its (nonzero) digits is 20412, while the sum is 39.

The square root of 21799209 is about 4668.9623044098. The cubic root of 21799209 is about 279.3488653740.

The spelling of 21799209 in words is "twenty-one million, seven hundred ninety-nine thousand, two hundred nine".