21388539 has 8 divisors (see below), whose sum is σ = 28879360. Its totient is φ = 14078376.

The previous prime is 21388529. The next prime is 21388541. The reversal of 21388539 is 93588312.

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

It is not a de Polignac number, because 21388539 - 2²⁴ = 4611323 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21388497 and 21388506.

It is not an unprimeable number, because it can be changed into a prime (21388529) 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, 44887 + ... + 45360.

It is an arithmetic number, because the mean of its divisors is an integer number (3609920).

Almost surely, 2^21388539 is an apocalyptic number.

21388539 is a deficient number, since it is larger than the sum of its proper divisors (7490821).

21388539 is an equidigital number, since it uses as much as digits as its factorization.

21388539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90329.

The product of its digits is 51840, while the sum is 39.

The square root of 21388539 is about 4624.7744809882. The cubic root of 21388539 is about 277.5835378719.

The spelling of 21388539 in words is "twenty-one million, three hundred eighty-eight thousand, five hundred thirty-nine".