198991 has 4 divisors (see below), whose sum is σ = 214312. Its totient is φ = 183672.

The previous prime is 198977. The next prime is 198997. The reversal of 198991 is 199891.

198991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199891 = 47 ⋅4253.

It is a cyclic number.

It is not a de Polignac number, because 198991 - 2⁵ = 198959 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 198991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (198997) 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, 7641 + ... + 7666.

It is an arithmetic number, because the mean of its divisors is an integer number (53578).

2¹⁹⁸⁹⁹¹ is an apocalyptic number.

198991 is a deficient number, since it is larger than the sum of its proper divisors (15321).

198991 is a wasteful number, since it uses less digits than its factorization.

198991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15320.

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

The square root of 198991 is about 446.0840727935. The cubic root of 198991 is about 58.3818444533.

Subtracting 198991 from its reverse (199891), we obtain a square (900 = 30²).

It can be divided in two parts, 19899 and 1, that added together give a triangular number (19900 = T₁₉₉).

The spelling of 198991 in words is "one hundred ninety-eight thousand, nine hundred ninety-one".