21525439 has 12 divisors (see below), whose sum is σ = 23967048. Its totient is φ = 19217520.

The previous prime is 21525419. The next prime is 21525463. The reversal of 21525439 is 93452512.

It is not a de Polignac number, because 21525439 - 2⁵ = 21525407 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

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 21525439.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21525409) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11632 + ... + 13354.

It is an arithmetic number, because the mean of its divisors is an integer number (1997254).

Almost surely, 2^21525439 is an apocalyptic number.

21525439 is a deficient number, since it is larger than the sum of its proper divisors (2441609).

21525439 is a wasteful number, since it uses less digits than its factorization.

21525439 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1798 (or 1767 counting only the distinct ones).

The product of its digits is 10800, while the sum is 31.

The square root of 21525439 is about 4639.5515947126. The cubic root of 21525439 is about 278.1745147546.

The spelling of 21525439 in words is "twenty-one million, five hundred twenty-five thousand, four hundred thirty-nine".