1991831 has 4 divisors (see below), whose sum is σ = 1994664. Its totient is φ = 1989000.

The previous prime is 1991819. The next prime is 1991837. The reversal of 1991831 is 1381991.

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: 1381991 = 13 ⋅106307.

It is a cyclic number.

It is not a de Polignac number, because 1991831 - 2¹⁸ = 1729687 is a prime.

It is a super-2 number, since 2×1991831² = 7934781465122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991837) 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, 536 + ... + 2066.

It is an arithmetic number, because the mean of its divisors is an integer number (498666).

2^1991831 is an apocalyptic number.

1991831 is a deficient number, since it is larger than the sum of its proper divisors (2833).

1991831 is a wasteful number, since it uses less digits than its factorization.

1991831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2832.

The product of its digits is 1944, while the sum is 32.

The square root of 1991831 is about 1411.3224294965. The cubic root of 1991831 is about 125.8203326578.

The spelling of 1991831 in words is "one million, nine hundred ninety-one thousand, eight hundred thirty-one".