21331231 has 4 divisors (see below), whose sum is σ = 21343264. Its totient is φ = 21319200.

The previous prime is 21331217. The next prime is 21331267. The reversal of 21331231 is 13213312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21331231 - 2⁷ = 21331103 is a prime.

It is a super-2 number, since 2×21331231² = 910042831950722, 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 (21331201) 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, 2775 + ... + 7096.

It is an arithmetic number, because the mean of its divisors is an integer number (5335816).

Almost surely, 2^21331231 is an apocalyptic number.

21331231 is a deficient number, since it is larger than the sum of its proper divisors (12033).

21331231 is an equidigital number, since it uses as much as digits as its factorization.

21331231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12032.

The product of its digits is 108, while the sum is 16.

The square root of 21331231 is about 4618.5745636506. The cubic root of 21331231 is about 277.3353989627.

Adding to 21331231 its reverse (13213312), we get a palindrome (34544543).

It can be divided in two parts, 2133 and 1231, that added together give a square (3364 = 58²).

The spelling of 21331231 in words is "twenty-one million, three hundred thirty-one thousand, two hundred thirty-one".