21013231 has 4 divisors (see below), whose sum is σ = 21309264. Its totient is φ = 20717200.

The previous prime is 21013217. The next prime is 21013249. The reversal of 21013231 is 13231012.

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 21013231 - 2⁷ = 21013103 is a prime.

It is a super-2 number, since 2×21013231² = 883111754118722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21013271) 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, 147910 + ... + 148051.

It is an arithmetic number, because the mean of its divisors is an integer number (5327316).

Almost surely, 2^21013231 is an apocalyptic number.

21013231 is a deficient number, since it is larger than the sum of its proper divisors (296033).

21013231 is an equidigital number, since it uses as much as digits as its factorization.

21013231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 296032.

The product of its (nonzero) digits is 36, while the sum is 13.

The square root of 21013231 is about 4584.0190880929. The cubic root of 21013231 is about 275.9503472606.

Adding to 21013231 its reverse (13231012), we get a palindrome (34244243).

The spelling of 21013231 in words is "twenty-one million, thirteen thousand, two hundred thirty-one".