21331999 has 16 divisors (see below), whose sum is σ = 24285184. Its totient is φ = 18597600.

The previous prime is 21331993. The next prime is 21332009. The reversal of 21331999 is 99913312.

It is a cyclic number.

It is not a de Polignac number, because 21331999 - 2⁹ = 21331487 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 (21331993) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16714 + ... + 17944.

It is an arithmetic number, because the mean of its divisors is an integer number (1517824).

Almost surely, 2^21331999 is an apocalyptic number.

21331999 is a deficient number, since it is larger than the sum of its proper divisors (2953185).

21331999 is a wasteful number, since it uses less digits than its factorization.

21331999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1318.

The product of its digits is 13122, while the sum is 37.

The square root of 21331999 is about 4618.6577054378. The cubic root of 21331999 is about 277.3387272756.

The spelling of 21331999 in words is "twenty-one million, three hundred thirty-one thousand, nine hundred ninety-nine".