209805 has 16 divisors (see below), whose sum is σ = 342144. Its totient is φ = 109760.

The previous prime is 209801. The next prime is 209809. The reversal of 209805 is 508902.

It is an interprime number because it is at equal distance from previous prime (209801) and next prime (209809).

It is not a de Polignac number, because 209805 - 2² = 209801 is a prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209801) 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, 967 + ... + 1163.

It is an arithmetic number, because the mean of its divisors is an integer number (21384).

2²⁰⁹⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

209805 is a deficient number, since it is larger than the sum of its proper divisors (132339).

209805 is a wasteful number, since it uses less digits than its factorization.

209805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 276.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 209805 is about 458.0447576384. The cubic root of 209805 is about 59.4208159765.

The spelling of 209805 in words is "two hundred nine thousand, eight hundred five".