28509 has 16 divisors (see below), whose sum is σ = 44352. Its totient is φ = 16128.

The previous prime is 28499. The next prime is 28513. The reversal of 28509 is 90582.

It is not a de Polignac number, because 28509 - 2⁴ = 28493 is a prime.

28509 is a lucky number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28549) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 642 + ... + 684.

It is an arithmetic number, because the mean of its divisors is an integer number (2772).

2²⁸⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

28509 is a deficient number, since it is larger than the sum of its proper divisors (15843).

28509 is a wasteful number, since it uses less digits than its factorization.

28509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76.

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

The square root of 28509 is about 168.8460837568. The cubic root of 28509 is about 30.5487887066.

The spelling of 28509 in words is "twenty-eight thousand, five hundred nine".