8991 has 12 divisors (see below), whose sum is σ = 13832. Its totient is φ = 5832.

The previous prime is 8971. The next prime is 8999. The reversal of 8991 is 1998.

It is not a de Polignac number, because 8991 - 2⁷ = 8863 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8999) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 225 + ... + 261.

2⁸⁹⁹¹ is an apocalyptic number.

8991 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

8991 is a deficient number, since it is larger than the sum of its proper divisors (4841).

8991 is an equidigital number, since it uses as much as digits as its factorization.

8991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52 (or 40 counting only the distinct ones).

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

The square root of 8991 is about 94.8208837757. The cubic root of 8991 is about 20.7939023053.

8991 divided by its sum of digits (27) gives a palindrome (333).

It can be divided in two parts, 899 and 1, that added together give a square (900 = 30²).

The spelling of 8991 in words is "eight thousand, nine hundred ninety-one".