21312331 has 4 divisors (see below), whose sum is σ = 21323664. Its totient is φ = 21301000.

The previous prime is 21312323. The next prime is 21312337. The reversal of 21312331 is 13321312.

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 21312331 - 2³ = 21312323 is a prime.

It is a super-2 number, since 2×21312331² = 908430905307122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312337) 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, 2095 + ... + 6856.

It is an arithmetic number, because the mean of its divisors is an integer number (5330916).

Almost surely, 2^21312331 is an apocalyptic number.

21312331 is a deficient number, since it is larger than the sum of its proper divisors (11333).

21312331 is an equidigital number, since it uses as much as digits as its factorization.

21312331 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11332.

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

The square root of 21312331 is about 4616.5280243924. The cubic root of 21312331 is about 277.2534660779.

Adding to 21312331 its reverse (13321312), we get a palindrome (34633643).

It can be divided in two parts, 213 and 12331, that added together give a square (12544 = 112²).

The spelling of 21312331 in words is "twenty-one million, three hundred twelve thousand, three hundred thirty-one".