21645139 has 4 divisors (see below), whose sum is σ = 22586256. Its totient is φ = 20704024.

The previous prime is 21645133. The next prime is 21645167. The reversal of 21645139 is 93154612.

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 21645139 - 2⁹ = 21644627 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21645139.

It is not an unprimeable number, because it can be changed into a prime (21645133) 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, 470524 + ... + 470569.

It is an arithmetic number, because the mean of its divisors is an integer number (5646564).

Almost surely, 2^21645139 is an apocalyptic number.

21645139 is a deficient number, since it is larger than the sum of its proper divisors (941117).

21645139 is an equidigital number, since it uses as much as digits as its factorization.

21645139 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 941116.

The product of its digits is 6480, while the sum is 31.

The square root of 21645139 is about 4652.4336642235. The cubic root of 21645139 is about 278.6891919616.

The spelling of 21645139 in words is "twenty-one million, six hundred forty-five thousand, one hundred thirty-nine".