31821 has 4 divisors (see below), whose sum is σ = 42432. Its totient is φ = 21212.

The previous prime is 31817. The next prime is 31847. The reversal of 31821 is 12813.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12813 = 3 ⋅4271.

It is a cyclic number.

It is not a de Polignac number, because 31821 - 2² = 31817 is a prime.

It is a D-number.

It is a nialpdrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 31821.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 31821.

It is not an unprimeable number, because it can be changed into a prime (31891) 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, 5301 + ... + 5306.

It is an arithmetic number, because the mean of its divisors is an integer number (10608).

2³¹⁸²¹ is an apocalyptic number.

It is an amenable number.

31821 is a deficient number, since it is larger than the sum of its proper divisors (10611).

31821 is a wasteful number, since it uses less digits than its factorization.

31821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10610.

The product of its digits is 48, while the sum is 15.

The square root of 31821 is about 178.3844163597. The cubic root of 31821 is about 31.6887134867.

The spelling of 31821 in words is "thirty-one thousand, eight hundred twenty-one".