21540439 has 2 divisors, whose sum is σ = 21540440. Its totient is φ = 21540438.

The previous prime is 21540437. The next prime is 21540473. The reversal of 21540439 is 93404512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21540439 - 2¹ = 21540437 is a prime.

Together with 21540437, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21540437) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10770219 + 10770220.

It is an arithmetic number, because the mean of its divisors is an integer number (10770220).

Almost surely, 2^21540439 is an apocalyptic number.

21540439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21540439 is an equidigital number, since it uses as much as digits as its factorization.

21540439 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 21540439 is about 4641.1678487208. The cubic root of 21540439 is about 278.2391150455.

The spelling of 21540439 in words is "twenty-one million, five hundred forty thousand, four hundred thirty-nine".