21312431 has 4 divisors (see below), whose sum is σ = 24357072. Its totient is φ = 18267792.

The previous prime is 21312427. The next prime is 21312437. The reversal of 21312431 is 13421312.

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 21312431 - 2² = 21312427 is a prime.

It is a super-2 number, since 2×21312431² = 908439430259522, 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 (21312437) 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, 1522310 + ... + 1522323.

It is an arithmetic number, because the mean of its divisors is an integer number (6089268).

Almost surely, 2^21312431 is an apocalyptic number.

21312431 is a deficient number, since it is larger than the sum of its proper divisors (3044641).

21312431 is an equidigital number, since it uses as much as digits as its factorization.

21312431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3044640.

The product of its digits is 144, while the sum is 17.

The square root of 21312431 is about 4616.5388550298. The cubic root of 21312431 is about 277.2538997127.

Adding to 21312431 its reverse (13421312), we get a palindrome (34733743).

The spelling of 21312431 in words is "twenty-one million, three hundred twelve thousand, four hundred thirty-one".