21005439 has 16 divisors (see below), whose sum is σ = 34470912. Its totient is φ = 11079648.

The previous prime is 21005423. The next prime is 21005441. The reversal of 21005439 is 93450012.

It is not a de Polignac number, because 21005439 - 2⁴ = 21005423 is a prime.

21005439 is a modest number, since divided by 5439 gives 21 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005339) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38199 + ... + 38744.

It is an arithmetic number, because the mean of its divisors is an integer number (2154432).

Almost surely, 2^21005439 is an apocalyptic number.

21005439 is a deficient number, since it is larger than the sum of its proper divisors (13465473).

21005439 is a wasteful number, since it uses less digits than its factorization.

21005439 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76966.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21005439 is about 4583.1691000878. The cubic root of 21005439 is about 275.9162342941.

The spelling of 21005439 in words is "twenty-one million, five thousand, four hundred thirty-nine".