21705239 has 16 divisors (see below), whose sum is σ = 24161280. Its totient is φ = 19414080.

The previous prime is 21705227. The next prime is 21705241. The reversal of 21705239 is 93250712.

It is a cyclic number.

It is not a de Polignac number, because 21705239 - 2⁴ = 21705223 is a prime.

It is a super-2 number, since 2×21705239² = 942234800094242, which contains 22 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 (21705269) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24899 + ... + 25755.

It is an arithmetic number, because the mean of its divisors is an integer number (1510080).

Almost surely, 2^21705239 is an apocalyptic number.

21705239 is a deficient number, since it is larger than the sum of its proper divisors (2456041).

21705239 is a wasteful number, since it uses less digits than its factorization.

21705239 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 950.

The product of its (nonzero) digits is 3780, while the sum is 29.

The square root of 21705239 is about 4658.8881720857. Note that the first 3 decimals coincide. The cubic root of 21705239 is about 278.9468901961.

The spelling of 21705239 in words is "twenty-one million, seven hundred five thousand, two hundred thirty-nine".