1991591 has 8 divisors (see below), whose sum is σ = 2298240. Its totient is φ = 1690488.

The previous prime is 1991573. The next prime is 1991597. The reversal of 1991591 is 1951991.

1991591 is nontrivially palindromic in base 8.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1991591 - 2⁶ = 1991527 is a prime.

It is a super-2 number, since 2×1991591² = 7932869422562, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991597) 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 7 ways as a sum of consecutive naturals, for example, 581 + ... + 2078.

It is an arithmetic number, because the mean of its divisors is an integer number (287280).

2^1991591 is an apocalyptic number.

1991591 is a deficient number, since it is larger than the sum of its proper divisors (306649).

1991591 is a wasteful number, since it uses less digits than its factorization.

1991591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2773.

The product of its digits is 3645, while the sum is 35.

The square root of 1991591 is about 1411.2374002981. The cubic root of 1991591 is about 125.8152790007.

The spelling of 1991591 in words is "one million, nine hundred ninety-one thousand, five hundred ninety-one".