21791239 has 4 divisors (see below), whose sum is σ = 22298056. Its totient is φ = 21284424.

The previous prime is 21791227. The next prime is 21791257. The reversal of 21791239 is 93219712.

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 21791239 - 2¹¹ = 21789191 is a prime.

It is a super-5 number, since 5×21791239⁵ (a number of 38 digits) contains 55555 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21791219) 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, 253344 + ... + 253429.

It is an arithmetic number, because the mean of its divisors is an integer number (5574514).

Almost surely, 2^21791239 is an apocalyptic number.

21791239 is a deficient number, since it is larger than the sum of its proper divisors (506817).

21791239 is an equidigital number, since it uses as much as digits as its factorization.

21791239 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 506816.

The product of its digits is 6804, while the sum is 34.

The square root of 21791239 is about 4668.1087176714. The cubic root of 21791239 is about 279.3148170156.

The spelling of 21791239 in words is "twenty-one million, seven hundred ninety-one thousand, two hundred thirty-nine".