309805 has 4 divisors (see below), whose sum is σ = 371772. Its totient is φ = 247840.

The previous prime is 309797. The next prime is 309811. The reversal of 309805 is 508903.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 198916 + 110889 = 446^2 + 333^2 .

It is not a de Polignac number, because 309805 - 2³ = 309797 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 309805.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30976 + ... + 30985.

It is an arithmetic number, because the mean of its divisors is an integer number (92943).

2³⁰⁹⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

309805 is a deficient number, since it is larger than the sum of its proper divisors (61967).

309805 is an equidigital number, since it uses as much as digits as its factorization.

309805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61966.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 309805 is about 556.6012935666. The cubic root of 309805 is about 67.6648007876.

The spelling of 309805 in words is "three hundred nine thousand, eight hundred five".