9891 has 12 divisors (see below), whose sum is σ = 16432. Its totient is φ = 5616.

The previous prime is 9887. The next prime is 9901. The reversal of 9891 is 1989.

9891 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 9891 - 2² = 9887 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (9811) 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 11 ways as a sum of consecutive naturals, for example, 16 + ... + 141.

2⁹⁸⁹¹ is an apocalyptic number.

9891 is a deficient number, since it is larger than the sum of its proper divisors (6541).

9891 is a wasteful number, since it uses less digits than its factorization.

9891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 170 (or 167 counting only the distinct ones).

The product of its digits is 648, while the sum is 27.

The square root of 9891 is about 99.4535067255. The cubic root of 9891 is about 21.4657829624.

It can be divided in two parts, 989 and 1, that added together give a triangular number (990 = T₄₄).

The spelling of 9891 in words is "nine thousand, eight hundred ninety-one".