16821 has 16 divisors (see below), whose sum is σ = 28800. Its totient is φ = 9504.

The previous prime is 16811. The next prime is 16823. The reversal of 16821 is 12861.

It is not a de Polignac number, because 16821 - 2⁷ = 16693 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 16794 and 16803.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16823) 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 15 ways as a sum of consecutive naturals, for example, 145 + ... + 233.

It is an arithmetic number, because the mean of its divisors is an integer number (1800).

2¹⁶⁸²¹ is an apocalyptic number.

It is an amenable number.

16821 is a deficient number, since it is larger than the sum of its proper divisors (11979).

16821 is an equidigital number, since it uses as much as digits as its factorization.

16821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105 (or 99 counting only the distinct ones).

The product of its digits is 96, while the sum is 18.

The square root of 16821 is about 129.6957979273. The cubic root of 16821 is about 25.6222503494.

The spelling of 16821 in words is "sixteen thousand, eight hundred twenty-one".