21521539 has 8 divisors (see below), whose sum is σ = 23523920. Its totient is φ = 19568736.

The previous prime is 21521527. The next prime is 21521557. The reversal of 21521539 is 93512512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521539 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521579) 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, 11484 + ... + 13225.

It is an arithmetic number, because the mean of its divisors is an integer number (2940490).

Almost surely, 2^21521539 is an apocalyptic number.

21521539 is a deficient number, since it is larger than the sum of its proper divisors (2002381).

21521539 is a wasteful number, since it uses less digits than its factorization.

21521539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24789.

The product of its digits is 2700, while the sum is 28.

The square root of 21521539 is about 4639.1312764353. The cubic root of 21521539 is about 278.1577137634.

The spelling of 21521539 in words is "twenty-one million, five hundred twenty-one thousand, five hundred thirty-nine".