21311231 has 4 divisors (see below), whose sum is σ = 21379632. Its totient is φ = 21242832.

The previous prime is 21311219. The next prime is 21311237. The reversal of 21311231 is 13211312.

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 21311231 - 2¹⁰ = 21310207 is a prime.

It is a super-2 number, since 2×21311231² = 908337133470722, 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 (21311237) 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, 33731 + ... + 34356.

It is an arithmetic number, because the mean of its divisors is an integer number (5344908).

Almost surely, 2^21311231 is an apocalyptic number.

21311231 is a deficient number, since it is larger than the sum of its proper divisors (68401).

21311231 is an equidigital number, since it uses as much as digits as its factorization.

21311231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68400.

The product of its digits is 36, while the sum is 14.

The square root of 21311231 is about 4616.4088857033. The cubic root of 21311231 is about 277.2486960059.

Adding to 21311231 its reverse (13211312), we get a palindrome (34522543).

The spelling of 21311231 in words is "twenty-one million, three hundred eleven thousand, two hundred thirty-one".