21521039 has 4 divisors (see below), whose sum is σ = 21690624. Its totient is φ = 21351456.

The previous prime is 21521033. The next prime is 21521041. The reversal of 21521039 is 93012512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521039 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521033) 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 3 ways as a sum of consecutive naturals, for example, 84602 + ... + 84855.

It is an arithmetic number, because the mean of its divisors is an integer number (5422656).

Almost surely, 2^21521039 is an apocalyptic number.

21521039 is a deficient number, since it is larger than the sum of its proper divisors (169585).

21521039 is a wasteful number, since it uses less digits than its factorization.

21521039 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 169584.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21521039 is about 4639.0773867225. The cubic root of 21521039 is about 278.1555596434.

The spelling of 21521039 in words is "twenty-one million, five hundred twenty-one thousand, thirty-nine".