21899 has 4 divisors (see below), whose sum is σ = 22320. Its totient is φ = 21480.

The previous prime is 21893. The next prime is 21911. The reversal of 21899 is 99812.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21899 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21893) 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, 119 + ... + 240.

It is an arithmetic number, because the mean of its divisors is an integer number (5580).

2²¹⁸⁹⁹ is an apocalyptic number.

21899 is a deficient number, since it is larger than the sum of its proper divisors (421).

21899 is an equidigital number, since it uses as much as digits as its factorization.

21899 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 420.

The product of its digits is 1296, while the sum is 29.

The square root of 21899 is about 147.9831071440. The cubic root of 21899 is about 27.9774478270.

It can be divided in two parts, 2189 and 9, that multiplied together give a triangular number (19701 = T₁₉₈).

The spelling of 21899 in words is "twenty-one thousand, eight hundred ninety-nine".