991917 has 12 divisors (see below), whose sum is σ = 1441440. Its totient is φ = 657288.

The previous prime is 991909. The next prime is 991927. The reversal of 991917 is 719199.

It is not a de Polignac number, because 991917 - 2³ = 991909 is a prime.

991917 is a lucky number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991917.

It is not an unprimeable number, because it can be changed into a prime (991927) 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 11 ways as a sum of consecutive naturals, for example, 2584 + ... + 2942.

It is an arithmetic number, because the mean of its divisors is an integer number (120120).

2⁹⁹¹⁹¹⁷ is an apocalyptic number.

It is an amenable number.

991917 is a deficient number, since it is larger than the sum of its proper divisors (449523).

991917 is a wasteful number, since it uses less digits than its factorization.

991917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 672 (or 669 counting only the distinct ones).

The product of its digits is 5103, while the sum is 36.

The square root of 991917 is about 995.9502999648. The cubic root of 991917 is about 99.7298374459.

It can be divided in two parts, 99 and 1917, that added together give a triangular number (2016 = T₆₃).

The spelling of 991917 in words is "nine hundred ninety-one thousand, nine hundred seventeen".