20931 has 4 divisors (see below), whose sum is σ = 27912. Its totient is φ = 13952.

The previous prime is 20929. The next prime is 20939. The reversal of 20931 is 13902.

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 20931 - 2¹ = 20929 is a prime.

It is a super-2 number, since 2×20931² = 876213522, which contains 22 as substring.

It is a D-number.

It is a self number, because there is not a number n which added to its sum of digits gives 20931.

It is not an unprimeable number, because it can be changed into a prime (20939) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3486 + ... + 3491.

It is an arithmetic number, because the mean of its divisors is an integer number (6978).

2²⁰⁹³¹ is an apocalyptic number.

20931 is the 92-nd centered pentagonal number.

20931 is a deficient number, since it is larger than the sum of its proper divisors (6981).

20931 is an equidigital number, since it uses as much as digits as its factorization.

20931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6980.

The product of its (nonzero) digits is 54, while the sum is 15.

The square root of 20931 is about 144.6754989623. The cubic root of 20931 is about 27.5589918201.

The spelling of 20931 in words is "twenty thousand, nine hundred thirty-one".