21305899 has 4 divisors (see below), whose sum is σ = 21759264. Its totient is φ = 20852536.

The previous prime is 21305891. The next prime is 21305909. The reversal of 21305899 is 99850312.

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

It is a cyclic number.

It is not a de Polignac number, because 21305899 - 2³ = 21305891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21305891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 226612 + ... + 226705.

It is an arithmetic number, because the mean of its divisors is an integer number (5439816).

Almost surely, 2^21305899 is an apocalyptic number.

21305899 is a deficient number, since it is larger than the sum of its proper divisors (453365).

21305899 is an equidigital number, since it uses as much as digits as its factorization.

21305899 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 453364.

The product of its (nonzero) digits is 19440, while the sum is 37.

The square root of 21305899 is about 4615.8313444059. The cubic root of 21305899 is about 277.2255718396.

The spelling of 21305899 in words is "twenty-one million, three hundred five thousand, eight hundred ninety-nine".