13821 has 8 divisors (see below), whose sum is σ = 19584. Its totient is φ = 8640.

The previous prime is 13807. The next prime is 13829. The reversal of 13821 is 12831.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 13821 - 2⁵ = 13789 is a prime.

13821 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 13821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (13829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 85 + ... + 186.

It is an arithmetic number, because the mean of its divisors is an integer number (2448).

2¹³⁸²¹ is an apocalyptic number.

It is an amenable number.

13821 is a deficient number, since it is larger than the sum of its proper divisors (5763).

13821 is a wasteful number, since it uses less digits than its factorization.

13821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 291.

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

The square root of 13821 is about 117.5627492023. The cubic root of 13821 is about 23.9982637633.

Subtracting from 13821 its reverse (12831), we obtain a triangular number (990 = T₄₄).

The spelling of 13821 in words is "thirteen thousand, eight hundred twenty-one".