180991 has 4 divisors (see below), whose sum is σ = 181984. Its totient is φ = 180000.

The previous prime is 180959. The next prime is 181001. The reversal of 180991 is 199081.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a 5-Lehmer number, since φ(180991) divides (180991-1)⁵.

It is a cyclic number.

It is not a de Polignac number, because 180991 - 2⁵ = 180959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (180391) 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, 135 + ... + 616.

It is an arithmetic number, because the mean of its divisors is an integer number (45496).

2¹⁸⁰⁹⁹¹ is an apocalyptic number.

180991 is a deficient number, since it is larger than the sum of its proper divisors (993).

180991 is an equidigital number, since it uses as much as digits as its factorization.

180991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 992.

The product of its (nonzero) digits is 648, while the sum is 28.

The square root of 180991 is about 425.4303703310. The cubic root of 180991 is about 56.5655906759.

The spelling of 180991 in words is "one hundred eighty thousand, nine hundred ninety-one".