21312731 has 16 divisors (see below), whose sum is σ = 23950080. Its totient is φ = 18801120.

The previous prime is 21312727. The next prime is 21312751. The reversal of 21312731 is 13721312.

It is a cyclic number.

It is not a de Polignac number, because 21312731 - 2² = 21312727 is a prime.

It is a super-2 number, since 2×21312731² = 908465005356722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21312721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 80906 + ... + 81168.

It is an arithmetic number, because the mean of its divisors is an integer number (1496880).

Almost surely, 2^21312731 is an apocalyptic number.

21312731 is a deficient number, since it is larger than the sum of its proper divisors (2637349).

21312731 is a wasteful number, since it uses less digits than its factorization.

21312731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 466.

The product of its digits is 252, while the sum is 20.

The square root of 21312731 is about 4616.5713467897. The cubic root of 21312731 is about 277.2552006089.

The spelling of 21312731 in words is "twenty-one million, three hundred twelve thousand, seven hundred thirty-one".