918991 has 4 divisors (see below), whose sum is σ = 938592. Its totient is φ = 899392.

The previous prime is 918989. The next prime is 919013. The reversal of 918991 is 199819.

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

It is not a de Polignac number, because 918991 - 2¹ = 918989 is a prime.

It is a Duffinian number.

918991 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 918991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (918971) 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, 9730 + ... + 9823.

It is an arithmetic number, because the mean of its divisors is an integer number (234648).

2⁹¹⁸⁹⁹¹ is an apocalyptic number.

918991 is a deficient number, since it is larger than the sum of its proper divisors (19601).

918991 is a wasteful number, since it uses less digits than its factorization.

918991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19600.

The product of its digits is 5832, while the sum is 37.

The square root of 918991 is about 958.6401827589. The cubic root of 918991 is about 97.2233137413.

The spelling of 918991 in words is "nine hundred eighteen thousand, nine hundred ninety-one".