816991 has 8 divisors (see below), whose sum is σ = 942080. Its totient is φ = 694008.

The previous prime is 816971. The next prime is 817013. The reversal of 816991 is 199618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 816991 - 2¹¹ = 814943 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 (816911) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 430 + ... + 1348.

It is an arithmetic number, because the mean of its divisors is an integer number (117760).

2⁸¹⁶⁹⁹¹ is an apocalyptic number.

816991 is a deficient number, since it is larger than the sum of its proper divisors (125089).

816991 is a wasteful number, since it uses less digits than its factorization.

816991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1053.

The product of its digits is 3888, while the sum is 34.

The square root of 816991 is about 903.8755445303. The cubic root of 816991 is about 93.4843883302.

The spelling of 816991 in words is "eight hundred sixteen thousand, nine hundred ninety-one".