21390239 has 8 divisors (see below), whose sum is σ = 23171232. Its totient is φ = 19628640.

The previous prime is 21390163. The next prime is 21390247. The reversal of 21390239 is 93209312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21390239 - 2²⁴ = 4613023 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 (21390289) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2507 + ... + 7004.

It is an arithmetic number, because the mean of its divisors is an integer number (2896404).

Almost surely, 2^21390239 is an apocalyptic number.

21390239 is a deficient number, since it is larger than the sum of its proper divisors (1780993).

21390239 is a wasteful number, since it uses less digits than its factorization.

21390239 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9697.

The product of its (nonzero) digits is 2916, while the sum is 29.

The square root of 21390239 is about 4624.9582700820. The cubic root of 21390239 is about 277.5908919587.

The spelling of 21390239 in words is "twenty-one million, three hundred ninety thousand, two hundred thirty-nine".