1991791 has 4 divisors (see below), whose sum is σ = 2002000. Its totient is φ = 1981584.

The previous prime is 1991779. The next prime is 1991797. The reversal of 1991791 is 1971991.

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 1991791 - 2⁹ = 1991279 is a prime.

It is a Duffinian number.

1991791 is a modest number, since divided by 1791 gives 199 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 1991791.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991797) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4806 + ... + 5203.

It is an arithmetic number, because the mean of its divisors is an integer number (500500).

2^1991791 is an apocalyptic number.

1991791 is a deficient number, since it is larger than the sum of its proper divisors (10209).

1991791 is a wasteful number, since it uses less digits than its factorization.

1991791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10208.

The product of its digits is 5103, while the sum is 37.

The square root of 1991791 is about 1411.3082583192. The cubic root of 1991791 is about 125.8194904098.

It can be divided in two parts, 199 and 1791, that multiplied together give a square (356409 = 597²).

The spelling of 1991791 in words is "one million, nine hundred ninety-one thousand, seven hundred ninety-one".