165809 has 4 divisors (see below), whose sum is σ = 189504. Its totient is φ = 142116.

The previous prime is 165799. The next prime is 165811. The reversal of 165809 is 908561.

165809 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 908561 = 19 ⋅47819.

It is a cyclic number.

It is not a de Polignac number, because 165809 - 2⁸ = 165553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (165829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11837 + ... + 11850.

It is an arithmetic number, because the mean of its divisors is an integer number (47376).

2¹⁶⁵⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

165809 is a deficient number, since it is larger than the sum of its proper divisors (23695).

165809 is an equidigital number, since it uses as much as digits as its factorization.

165809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23694.

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 165809 is about 407.1965127552. The cubic root of 165809 is about 54.9375599944.

The spelling of 165809 in words is "one hundred sixty-five thousand, eight hundred nine".