21840239 has 4 divisors (see below), whose sum is σ = 22147920. Its totient is φ = 21532560.

The previous prime is 21840209. The next prime is 21840241. The reversal of 21840239 is 93204812.

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-21840239 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 (21840209) 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, 153734 + ... + 153875.

It is an arithmetic number, because the mean of its divisors is an integer number (5536980).

Almost surely, 2^21840239 is an apocalyptic number.

21840239 is a deficient number, since it is larger than the sum of its proper divisors (307681).

21840239 is an equidigital number, since it uses as much as digits as its factorization.

21840239 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 307680.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 21840239 is about 4673.3541487886. The cubic root of 21840239 is about 279.5240169966.

The spelling of 21840239 in words is "twenty-one million, eight hundred forty thousand, two hundred thirty-nine".