21243839 has 6 divisors (see below), whose sum is σ = 21582504. Its totient is φ = 20906340.

The previous prime is 21243823. The next prime is 21243841. The reversal of 21243839 is 93834212.

It is a happy number.

It is not a de Polignac number, because 21243839 - 2⁴ = 21243823 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 (21243139) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 38564 + ... + 39110.

It is an arithmetic number, because the mean of its divisors is an integer number (3597084).

Almost surely, 2^21243839 is an apocalyptic number.

21243839 is a deficient number, since it is larger than the sum of its proper divisors (338665).

21243839 is an frugal number, since it uses more digits than its factorization.

21243839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1165 (or 618 counting only the distinct ones).

The product of its digits is 10368, while the sum is 32.

The square root of 21243839 is about 4609.1039259275. The cubic root of 21243839 is about 276.9561417527.

The spelling of 21243839 in words is "twenty-one million, two hundred forty-three thousand, eight hundred thirty-nine".