1991111 has 4 divisors (see below), whose sum is σ = 2059800. Its totient is φ = 1922424.

The previous prime is 1991107. The next prime is 1991123. The reversal of 1991111 is 1111991.

It is a happy number.

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 1991111 - 2² = 1991107 is a prime.

It is a Duffinian number.

1991111 is a modest number, since divided by 1111 gives 199 as remainder.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991131) 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, 34301 + ... + 34358.

It is an arithmetic number, because the mean of its divisors is an integer number (514950).

2^1991111 is an apocalyptic number.

1991111 is a deficient number, since it is larger than the sum of its proper divisors (68689).

1991111 is an equidigital number, since it uses as much as digits as its factorization.

1991111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68688.

The product of its digits is 81, while the sum is 23.

The square root of 1991111 is about 1411.0673265298. The cubic root of 1991111 is about 125.8051704683.

The spelling of 1991111 in words is "one million, nine hundred ninety-one thousand, one hundred eleven".