199837991 has 4 divisors (see below), whose sum is σ = 210355800. Its totient is φ = 189320184.

The previous prime is 199837987. The next prime is 199838003. The reversal of 199837991 is 199738991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199738991 = 7549 ⋅26459.

It is a cyclic number.

It is not a de Polignac number, because 199837991 - 2² = 199837987 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 (199837951) 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, 5258876 + ... + 5258913.

It is an arithmetic number, because the mean of its divisors is an integer number (52588950).

Almost surely, 2^199837991 is an apocalyptic number.

199837991 is a deficient number, since it is larger than the sum of its proper divisors (10517809).

199837991 is a wasteful number, since it uses less digits than its factorization.

199837991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10517808.

The product of its digits is 1102248, while the sum is 56.

The square root of 199837991 is about 14136.4065801745. The cubic root of 199837991 is about 584.6455992565.

The spelling of 199837991 in words is "one hundred ninety-nine million, eight hundred thirty-seven thousand, nine hundred ninety-one".