21312031 has 4 divisors (see below), whose sum is σ = 22951432. Its totient is φ = 19672632.

The previous prime is 21312023. The next prime is 21312059. The reversal of 21312031 is 13021312.

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 21312031 - 2³ = 21312023 is a prime.

It is a super-2 number, since 2×21312031² = 908405330689922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (13), and also a Moran number because the ratio is a prime number: 1639387 = 21312031 / (2 + 1 + 3 + 1 + 2 + 0 + 3 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312001) 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, 819681 + ... + 819706.

It is an arithmetic number, because the mean of its divisors is an integer number (5737858).

Almost surely, 2^21312031 is an apocalyptic number.

21312031 is a deficient number, since it is larger than the sum of its proper divisors (1639401).

21312031 is a wasteful number, since it uses less digits than its factorization.

21312031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1639400.

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

The square root of 21312031 is about 4616.4955323275. The cubic root of 21312031 is about 277.2521651655.

Adding to 21312031 its reverse (13021312), we get a palindrome (34333343).

The spelling of 21312031 in words is "twenty-one million, three hundred twelve thousand, thirty-one".