28521209 has 4 divisors (see below), whose sum is σ = 29441280. Its totient is φ = 27601140.

The previous prime is 28521203. The next prime is 28521217. The reversal of 28521209 is 90212582.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 28521209 - 2⁴ = 28521193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28521203) 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, 459989 + ... + 460050.

It is an arithmetic number, because the mean of its divisors is an integer number (7360320).

Almost surely, 2^28521209 is an apocalyptic number.

It is an amenable number.

28521209 is a deficient number, since it is larger than the sum of its proper divisors (920071).

28521209 is an equidigital number, since it uses as much as digits as its factorization.

28521209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 920070.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 28521209 is about 5340.5251614425. The cubic root of 28521209 is about 305.5314893124.

The spelling of 28521209 in words is "twenty-eight million, five hundred twenty-one thousand, two hundred nine".