21904139 has 4 divisors (see below), whose sum is σ = 22212720. Its totient is φ = 21595560.

The previous prime is 21904133. The next prime is 21904151. The reversal of 21904139 is 93140912.

It is a happy number.

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 21904139 - 2⁴ = 21904123 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21904133) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 154184 + ... + 154325.

It is an arithmetic number, because the mean of its divisors is an integer number (5553180).

Almost surely, 2^21904139 is an apocalyptic number.

21904139 is a deficient number, since it is larger than the sum of its proper divisors (308581).

21904139 is an equidigital number, since it uses as much as digits as its factorization.

21904139 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 308580.

The product of its (nonzero) digits is 1944, while the sum is 29.

The square root of 21904139 is about 4680.1857869106. The cubic root of 21904139 is about 279.7963612871.

The spelling of 21904139 in words is "twenty-one million, nine hundred four thousand, one hundred thirty-nine".