21013523 has 4 divisors (see below), whose sum is σ = 21249720. Its totient is φ = 20777328.

The previous prime is 21013511. The next prime is 21013529. The reversal of 21013523 is 32531012.

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 21013523 - 2⁴ = 21013507 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21013529) 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, 117965 + ... + 118142.

It is an arithmetic number, because the mean of its divisors is an integer number (5312430).

Almost surely, 2^21013523 is an apocalyptic number.

21013523 is a deficient number, since it is larger than the sum of its proper divisors (236197).

21013523 is an equidigital number, since it uses as much as digits as its factorization.

21013523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 236196.

The product of its (nonzero) digits is 180, while the sum is 17.

The square root of 21013523 is about 4584.0509377624. The cubic root of 21013523 is about 275.9516254573.

Adding to 21013523 its reverse (32531012), we get a palindrome (53544535).

The spelling of 21013523 in words is "twenty-one million, thirteen thousand, five hundred twenty-three".