199991 has 4 divisors (see below), whose sum is σ = 218184. Its totient is φ = 181800.

The previous prime is 199967. The next prime is 199999.

It is a happy number.

199991 is nontrivially palindromic in base 10.

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 199991 - 2¹⁰ = 198967 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 199991.

It is not an unprimeable number, because it can be changed into a prime (199999) 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, 9080 + ... + 9101.

It is an arithmetic number, because the mean of its divisors is an integer number (54546).

2¹⁹⁹⁹⁹¹ is an apocalyptic number.

199991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

199991 is a deficient number, since it is larger than the sum of its proper divisors (18193).

199991 is a wasteful number, since it uses less digits than its factorization.

199991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18192.

The product of its digits is 6561, while the sum is 38.

The square root of 199991 is about 447.2035330809. The cubic root of 199991 is about 58.4794775458.

The spelling of 199991 in words is "one hundred ninety-nine thousand, nine hundred ninety-one".