999109991 has 16 divisors (see below), whose sum is σ = 1111987968. Its totient is φ = 890092800.

The previous prime is 999109987. The next prime is 999110027. The reversal of 999109991 is 199901999.

It is a cyclic number.

It is not a de Polignac number, because 999109991 - 2² = 999109987 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 (999109921) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 105356 + ... + 114446.

It is an arithmetic number, because the mean of its divisors is an integer number (69499248).

Almost surely, 2^999109991 is an apocalyptic number.

999109991 is a deficient number, since it is larger than the sum of its proper divisors (112877977).

999109991 is a wasteful number, since it uses less digits than its factorization.

999109991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9302.

The product of its (nonzero) digits is 531441, while the sum is 56.

The square root of 999109991 is about 31608.7011912859. The cubic root of 999109991 is about 999.7032422769.

It can be divided in two parts, 99910 and 9991, that added together give a palindrome (109901).

The spelling of 999109991 in words is "nine hundred ninety-nine million, one hundred nine thousand, nine hundred ninety-one".