9821 has 8 divisors (see below), whose sum is σ = 11904. Its totient is φ = 7920.

The previous prime is 9817. The next prime is 9829. The reversal of 9821 is 1289.

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

It is a cyclic number.

It is not a de Polignac number, because 9821 - 2² = 9817 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a junction number, because it is equal to n+sod(n) for n = 9793 and 9802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9829) by changing a digit.

It is an upside-down number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 131 + ... + 191.

It is an arithmetic number, because the mean of its divisors is an integer number (1488).

2⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

9821 is a deficient number, since it is larger than the sum of its proper divisors (2083).

9821 is a wasteful number, since it uses less digits than its factorization.

9821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91.

The product of its digits is 144, while the sum is 20.

The square root of 9821 is about 99.1009586230. The cubic root of 9821 is about 21.4150242415.

Subtracting from 9821 its sum of digits (20), we obtain a square (9801 = 99²).

The spelling of 9821 in words is "nine thousand, eight hundred twenty-one".