509991 has 8 divisors (see below), whose sum is σ = 685440. Its totient is φ = 337272.

The previous prime is 509989. The next prime is 510007. The reversal of 509991 is 199905.

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

It is not a de Polignac number, because 509991 - 2¹ = 509989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (509911) 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, 195 + ... + 1028.

It is an arithmetic number, because the mean of its divisors is an integer number (85680).

2⁵⁰⁹⁹⁹¹ is an apocalyptic number.

509991 is a deficient number, since it is larger than the sum of its proper divisors (175449).

509991 is a wasteful number, since it uses less digits than its factorization.

509991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1365.

The product of its (nonzero) digits is 3645, while the sum is 33.

The square root of 509991 is about 714.1365415661. The cubic root of 509991 is about 79.8952274271.

The spelling of 509991 in words is "five hundred nine thousand, nine hundred ninety-one".