21118109 has 4 divisors (see below), whose sum is σ = 21145404. Its totient is φ = 21090816.

The previous prime is 21118103. The next prime is 21118129. The reversal of 21118109 is 90181112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15382084 + 5736025 = 3922^2 + 2395^2 .

It is a cyclic number.

It is not a de Polignac number, because 21118109 - 2⁴ = 21118093 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21118103) 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, 12452 + ... + 14045.

It is an arithmetic number, because the mean of its divisors is an integer number (5286351).

Almost surely, 2^21118109 is an apocalyptic number.

It is an amenable number.

21118109 is a deficient number, since it is larger than the sum of its proper divisors (27295).

21118109 is an equidigital number, since it uses as much as digits as its factorization.

21118109 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27294.

The product of its (nonzero) digits is 144, while the sum is 23.

The square root of 21118109 is about 4595.4443745953. Note that the first 3 decimals coincide. The cubic root of 21118109 is about 276.4086792002.

It can be divided in two parts, 2 and 1118109, that added together give a palindrome (1118111).

The spelling of 21118109 in words is "twenty-one million, one hundred eighteen thousand, one hundred nine".