21513539 has 4 divisors (see below), whose sum is σ = 22095024. Its totient is φ = 20932056.

The previous prime is 21513523. The next prime is 21513559. The reversal of 21513539 is 93531512.

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

It is a cyclic number.

It is not a de Polignac number, because 21513539 - 2⁴ = 21513523 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21513559) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 290687 + ... + 290760.

It is an arithmetic number, because the mean of its divisors is an integer number (5523756).

Almost surely, 2^21513539 is an apocalyptic number.

21513539 is a deficient number, since it is larger than the sum of its proper divisors (581485).

21513539 is an equidigital number, since it uses as much as digits as its factorization.

21513539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 581484.

The product of its digits is 4050, while the sum is 29.

The square root of 21513539 is about 4638.2689658967. The cubic root of 21513539 is about 278.1232438386.

The spelling of 21513539 in words is "twenty-one million, five hundred thirteen thousand, five hundred thirty-nine".