991591 has 4 divisors (see below), whose sum is σ = 1043800. Its totient is φ = 939384.

The previous prime is 991579. The next prime is 991603. The reversal of 991591 is 195199.

991591 is nontrivially palindromic in base 3.

991591 is an esthetic number in base 3, because in such base its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (991579) and next prime (991603).

It is a cyclic number.

It is not a de Polignac number, because 991591 - 2⁹ = 991079 is a prime.

It is a super-2 number, since 2×991591² = 1966505422562, 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 (991511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26076 + ... + 26113.

It is an arithmetic number, because the mean of its divisors is an integer number (260950).

2⁹⁹¹⁵⁹¹ is an apocalyptic number.

991591 is a deficient number, since it is larger than the sum of its proper divisors (52209).

991591 is a wasteful number, since it uses less digits than its factorization.

991591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52208.

The product of its digits is 3645, while the sum is 34.

The square root of 991591 is about 995.7866237302. The cubic root of 991591 is about 99.7189106280.

The spelling of 991591 in words is "nine hundred ninety-one thousand, five hundred ninety-one".