21013539 has 4 divisors (see below), whose sum is σ = 28018056. Its totient is φ = 14009024.

The previous prime is 21013537. The next prime is 21013543. The reversal of 21013539 is 93531012.

It is a happy number.

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 21013539 - 2¹ = 21013537 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21013537) 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, 3502254 + ... + 3502259.

It is an arithmetic number, because the mean of its divisors is an integer number (7004514).

Almost surely, 2^21013539 is an apocalyptic number.

21013539 is a deficient number, since it is larger than the sum of its proper divisors (7004517).

21013539 is an equidigital number, since it uses as much as digits as its factorization.

21013539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7004516.

The product of its (nonzero) digits is 810, while the sum is 24.

The square root of 21013539 is about 4584.0526829433. The cubic root of 21013539 is about 275.9516954952.

The spelling of 21013539 in words is "twenty-one million, thirteen thousand, five hundred thirty-nine".