991689 has 4 divisors (see below), whose sum is σ = 1322256. Its totient is φ = 661124.

The previous prime is 991663. The next prime is 991693. The reversal of 991689 is 986199.

991689 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 991689 - 2¹¹ = 989641 is a prime.

It is a D-number.

It is a Curzon number.

991689 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 991689.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991689.

It is not an unprimeable number, because it can be changed into a prime (991619) 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, 165279 + ... + 165284.

It is an arithmetic number, because the mean of its divisors is an integer number (330564).

2⁹⁹¹⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

991689 is a deficient number, since it is larger than the sum of its proper divisors (330567).

991689 is a wasteful number, since it uses less digits than its factorization.

991689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330566.

The product of its digits is 34992, while the sum is 42.

The square root of 991689 is about 995.8358298435. The cubic root of 991689 is about 99.7221956286.

The spelling of 991689 in words is "nine hundred ninety-one thousand, six hundred eighty-nine".