28991 has 4 divisors (see below), whose sum is σ = 29592. Its totient is φ = 28392.

The previous prime is 28979. The next prime is 29009. The reversal of 28991 is 19982.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 28991 - 2⁶ = 28927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 28991.

It is not an unprimeable number, because it can be changed into a prime (28901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 221 + ... + 326.

It is an arithmetic number, because the mean of its divisors is an integer number (7398).

2²⁸⁹⁹¹ is an apocalyptic number.

28991 is a deficient number, since it is larger than the sum of its proper divisors (601).

28991 is an equidigital number, since it uses as much as digits as its factorization.

28991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 600.

The product of its digits is 1296, while the sum is 29.

The square root of 28991 is about 170.2674366989. The cubic root of 28991 is about 30.7199896692.

Subtracting from 28991 its reverse (19982), we obtain a palindrome (9009).

The spelling of 28991 in words is "twenty-eight thousand, nine hundred ninety-one".