199781791 has 4 divisors (see below), whose sum is σ = 217943784. Its totient is φ = 181619800.

The previous prime is 199781779. The next prime is 199781821. The reversal of 199781791 is 197187991.

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 199781791 - 2⁹ = 199781279 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 (199781711) 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, 9080980 + ... + 9081001.

It is an arithmetic number, because the mean of its divisors is an integer number (54485946).

Almost surely, 2^199781791 is an apocalyptic number.

199781791 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

199781791 is a deficient number, since it is larger than the sum of its proper divisors (18161993).

199781791 is a wasteful number, since it uses less digits than its factorization.

199781791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18161992.

The product of its digits is 285768, while the sum is 52.

The square root of 199781791 is about 14134.4186650884. The cubic root of 199781791 is about 584.5907879181.

The spelling of 199781791 in words is "one hundred ninety-nine million, seven hundred eighty-one thousand, seven hundred ninety-one".