189991 has 4 divisors (see below), whose sum is σ = 190912. Its totient is φ = 189072.

The previous prime is 189989. The next prime is 189997. The reversal of 189991 is 199981.

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, and also an emirpimes, since its reverse is a distinct semiprime: 199981 = 31 ⋅6451.

It is a cyclic number.

It is not a de Polignac number, because 189991 - 2¹ = 189989 is a prime.

It is a Duffinian number.

189991 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 189991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (189997) 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, 10 + ... + 616.

It is an arithmetic number, because the mean of its divisors is an integer number (47728).

2¹⁸⁹⁹⁹¹ is an apocalyptic number.

189991 is a deficient number, since it is larger than the sum of its proper divisors (921).

189991 is an equidigital number, since it uses as much as digits as its factorization.

189991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 920.

The product of its digits is 5832, while the sum is 37.

The square root of 189991 is about 435.8795705238. The cubic root of 189991 is about 57.4880630545.

The spelling of 189991 in words is "one hundred eighty-nine thousand, nine hundred ninety-one".