991888111 has 4 divisors (see below), whose sum is σ = 991951312. Its totient is φ = 991824912.

The previous prime is 991888109. The next prime is 991888129. The reversal of 991888111 is 111888199.

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: 111888199 = 1279 ⋅87481.

It is a cyclic number.

It is not a de Polignac number, because 991888111 - 2¹ = 991888109 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 (991880111) 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, 11926 + ... + 46108.

It is an arithmetic number, because the mean of its divisors is an integer number (247987828).

Almost surely, 2^991888111 is an apocalyptic number.

991888111 is a deficient number, since it is larger than the sum of its proper divisors (63201).

991888111 is a wasteful number, since it uses less digits than its factorization.

991888111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63200.

The product of its digits is 41472, while the sum is 46.

The square root of 991888111 is about 31494.2552063071. The cubic root of 991888111 is about 997.2886924552.

The spelling of 991888111 in words is "nine hundred ninety-one million, eight hundred eighty-eight thousand, one hundred eleven".