31921 has 4 divisors (see below), whose sum is σ = 32292. Its totient is φ = 31552.

The previous prime is 31907. The next prime is 31957. The reversal of 31921 is 12913.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12913 = 37 ⋅349.

It can be written as a sum of positive squares in 2 ways, for example, as 12321 + 19600 = 111^2 + 140^2 .

It is a cyclic number.

It is not a de Polignac number, because 31921 - 2⁷ = 31793 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 31895 and 31904.

It is not an unprimeable number, because it can be changed into a prime (31981) 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, 21 + ... + 253.

It is an arithmetic number, because the mean of its divisors is an integer number (8073).

2³¹⁹²¹ is an apocalyptic number.

31921 is the 96-th centered heptagonal number.

It is an amenable number.

31921 is a deficient number, since it is larger than the sum of its proper divisors (371).

31921 is a wasteful number, since it uses less digits than its factorization.

31921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 370.

The product of its digits is 54, while the sum is 16.

The square root of 31921 is about 178.6644900365. The cubic root of 31921 is about 31.7218735347.

The spelling of 31921 in words is "thirty-one thousand, nine hundred twenty-one".