21109 has 8 divisors (see below), whose sum is σ = 24480. Its totient is φ = 18000.

The previous prime is 21107. The next prime is 21121. The reversal of 21109 is 90112.

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

It is a cyclic number.

It is not a de Polignac number, because 21109 - 2¹ = 21107 is a prime.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21101) 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, 159 + ... + 259.

It is an arithmetic number, because the mean of its divisors is an integer number (3060).

2²¹¹⁰⁹ is an apocalyptic number.

It is an amenable number.

21109 is a deficient number, since it is larger than the sum of its proper divisors (3371).

21109 is a wasteful number, since it uses less digits than its factorization.

21109 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131.

The product of its (nonzero) digits is 18, while the sum is 13.

The square root of 21109 is about 145.2893664382. The cubic root of 21109 is about 27.6368931816.

It can be divided in two parts, 2 and 1109, that added together give a palindrome (1111).

The spelling of 21109 in words is "twenty-one thousand, one hundred nine".