21899209 has 4 divisors (see below), whose sum is σ = 21937104. Its totient is φ = 21861316.

The previous prime is 21899201. The next prime is 21899219. The reversal of 21899209 is 90299812.

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 21899209 - 2³ = 21899201 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21899201) 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 3 ways as a sum of consecutive naturals, for example, 18067 + ... + 19240.

It is an arithmetic number, because the mean of its divisors is an integer number (5484276).

Almost surely, 2^21899209 is an apocalyptic number.

It is an amenable number.

21899209 is a deficient number, since it is larger than the sum of its proper divisors (37895).

21899209 is an equidigital number, since it uses as much as digits as its factorization.

21899209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37894.

The product of its (nonzero) digits is 23328, while the sum is 40.

The square root of 21899209 is about 4679.6590687784. The cubic root of 21899209 is about 279.7753683054.

The spelling of 21899209 in words is "twenty-one million, eight hundred ninety-nine thousand, two hundred nine".