28009 has 4 divisors (see below), whose sum is σ = 28804. Its totient is φ = 27216.

The previous prime is 28001. The next prime is 28019. The reversal of 28009 is 90082.

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 21609 + 6400 = 147^2 + 80^2 .

It is a cyclic number.

It is not a de Polignac number, because 28009 - 2³ = 28001 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 8 and base 13.

It is not an unprimeable number, because it can be changed into a prime (28001) 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, 342 + ... + 415.

It is an arithmetic number, because the mean of its divisors is an integer number (7201).

2²⁸⁰⁰⁹ is an apocalyptic number.

It is an amenable number.

28009 is a deficient number, since it is larger than the sum of its proper divisors (795).

28009 is an equidigital number, since it uses as much as digits as its factorization.

28009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 794.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 28009 is about 167.3588957899. The cubic root of 28009 is about 30.3691428584.

It can be divided in two parts, 2800 and 9, that multiplied together give a triangular number (25200 = T₂₂₄).

The spelling of 28009 in words is "twenty-eight thousand, nine".