991865 has 16 divisors (see below), whose sum is σ = 1441152. Its totient is φ = 639744.

The previous prime is 991817. The next prime is 991867. The reversal of 991865 is 568199.

It is not a de Polignac number, because 991865 - 2¹⁰ = 990841 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991865.

It is not an unprimeable number, because it can be changed into a prime (991867) 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 15 ways as a sum of consecutive naturals, for example, 239 + ... + 1428.

It is an arithmetic number, because the mean of its divisors is an integer number (90072).

2⁹⁹¹⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

991865 is a deficient number, since it is larger than the sum of its proper divisors (449287).

991865 is a wasteful number, since it uses less digits than its factorization.

991865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1696.

The product of its digits is 19440, while the sum is 38.

The square root of 991865 is about 995.9241939023. The cubic root of 991865 is about 99.7280946784.

The spelling of 991865 in words is "nine hundred ninety-one thousand, eight hundred sixty-five".