818991 has 10 divisors (see below), whose sum is σ = 1223552. Its totient is φ = 545940.

The previous prime is 818977. The next prime is 818999. The reversal of 818991 is 199818.

It is not a de Polignac number, because 818991 - 2⁵ = 818959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (818999) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 4975 + ... + 5136.

2⁸¹⁸⁹⁹¹ is an apocalyptic number.

818991 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

818991 is a deficient number, since it is larger than the sum of its proper divisors (404561).

818991 is a wasteful number, since it uses less digits than its factorization.

818991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10123 (or 10114 counting only the distinct ones).

The product of its digits is 5184, while the sum is 36.

The square root of 818991 is about 904.9812152747. The cubic root of 818991 is about 93.5606096582.

The spelling of 818991 in words is "eight hundred eighteen thousand, nine hundred ninety-one".