209865 has 16 divisors (see below), whose sum is σ = 355968. Its totient is φ = 105216.

The previous prime is 209861. The next prime is 209887. The reversal of 209865 is 568902.

209865 = 103² + 104² + ... + 119².

It is not a de Polignac number, because 209865 - 2² = 209861 is a prime.

209865 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 209865.

It is not an unprimeable number, because it can be changed into a prime (209861) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 157 + ... + 666.

It is an arithmetic number, because the mean of its divisors is an integer number (22248).

2²⁰⁹⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

209865 is a deficient number, since it is larger than the sum of its proper divisors (146103).

209865 is a wasteful number, since it uses less digits than its factorization.

209865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 848.

The product of its (nonzero) digits is 4320, while the sum is 30.

The square root of 209865 is about 458.1102487393. The cubic root of 209865 is about 59.4264798217.

Adding to 209865 its product of nonzero digits (4320), we get a triangular number (214185 = T₆₅₄).

The spelling of 209865 in words is "two hundred nine thousand, eight hundred sixty-five".