21390439 has 4 divisors (see below), whose sum is σ = 24446224. Its totient is φ = 18334656.

The previous prime is 21390433. The next prime is 21390449. The reversal of 21390439 is 93409312.

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 21390439 - 2¹³ = 21382247 is a prime.

It is a super-2 number, since 2×21390439² = 915101761225442, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21390439.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390433) 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, 1527882 + ... + 1527895.

It is an arithmetic number, because the mean of its divisors is an integer number (6111556).

Almost surely, 2^21390439 is an apocalyptic number.

21390439 is a deficient number, since it is larger than the sum of its proper divisors (3055785).

21390439 is an equidigital number, since it uses as much as digits as its factorization.

21390439 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3055784.

The product of its (nonzero) digits is 5832, while the sum is 31.

The square root of 21390439 is about 4624.9798918482. The cubic root of 21390439 is about 277.5917571197.

The spelling of 21390439 in words is "twenty-one million, three hundred ninety thousand, four hundred thirty-nine".