21108909 has 4 divisors (see below), whose sum is σ = 28145216. Its totient is φ = 14072604.

The previous prime is 21108889. The next prime is 21108911. The reversal of 21108909 is 90980112.

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 21108909 - 2¹¹ = 21106861 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21108929) 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, 3518149 + ... + 3518154.

It is an arithmetic number, because the mean of its divisors is an integer number (7036304).

Almost surely, 2^21108909 is an apocalyptic number.

It is an amenable number.

21108909 is a deficient number, since it is larger than the sum of its proper divisors (7036307).

21108909 is an equidigital number, since it uses as much as digits as its factorization.

21108909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7036306.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 21108909 is about 4594.4432742172. The cubic root of 21108909 is about 276.3685346776.

The spelling of 21108909 in words is "twenty-one million, one hundred eight thousand, nine hundred nine".