21099 has 8 divisors (see below), whose sum is σ = 30352. Its totient is φ = 12960.

The previous prime is 21089. The next prime is 21101. The reversal of 21099 is 99012.

It is a happy number.

21099 is nontrivially palindromic in base 11.

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

It is not a de Polignac number, because 21099 - 2⁵ = 21067 is a prime.

It is a Duffinian number.

It is a plaindrome in base 5.

It is a zygodrome in base 5.

It is not an unprimeable number, because it can be changed into a prime (21019) 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, 232 + ... + 309.

It is an arithmetic number, because the mean of its divisors is an integer number (3794).

2²¹⁰⁹⁹ is an apocalyptic number.

21099 is the 78-th nonagonal number.

21099 is a deficient number, since it is larger than the sum of its proper divisors (9253).

21099 is a wasteful number, since it uses less digits than its factorization.

21099 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 557.

The product of its (nonzero) digits is 162, while the sum is 21.

The square root of 21099 is about 145.2549482806. The cubic root of 21099 is about 27.6325283359.

It can be divided in two parts, 2109 and 9, that multiplied together give a palindrome (18981).

The spelling of 21099 in words is "twenty-one thousand, ninety-nine".