809991 has 48 divisors (see below), whose sum is σ = 1537536. Its totient is φ = 399168.

The previous prime is 809983. The next prime is 809993. The reversal of 809991 is 199908.

809991 = 234² + 235² + ... + 247².

It is not a de Polignac number, because 809991 - 2³ = 809983 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (809993) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 18816 + ... + 18858.

It is an arithmetic number, because the mean of its divisors is an integer number (32032).

2⁸⁰⁹⁹⁹¹ is an apocalyptic number.

809991 is a deficient number, since it is larger than the sum of its proper divisors (727545).

809991 is a wasteful number, since it uses less digits than its factorization.

809991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92 (or 89 counting only the distinct ones).

The product of its (nonzero) digits is 5832, while the sum is 36.

The square root of 809991 is about 899.9949999861. The cubic root of 809991 is about 93.2166299293.

The spelling of 809991 in words is "eight hundred nine thousand, nine hundred ninety-one".