28187521 has 4 divisors (see below), whose sum is σ = 28478212. Its totient is φ = 27896832.

The previous prime is 28187491. The next prime is 28187527. The reversal of 28187521 is 12578182.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12578182 = 2 ⋅6289091.

It can be written as a sum of positive squares in 2 ways, for example, as 19713600 + 8473921 = 4440^2 + 2911^2 .

It is a cyclic number.

It is not a de Polignac number, because 28187521 - 2⁹ = 28187009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28187527) 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, 145200 + ... + 145393.

It is an arithmetic number, because the mean of its divisors is an integer number (7119553).

Almost surely, 2^28187521 is an apocalyptic number.

It is an amenable number.

28187521 is a deficient number, since it is larger than the sum of its proper divisors (290691).

28187521 is an equidigital number, since it uses as much as digits as its factorization.

28187521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 290690.

The product of its digits is 8960, while the sum is 34.

The square root of 28187521 is about 5309.1921231012. The cubic root of 28187521 is about 304.3352754384.

The spelling of 28187521 in words is "twenty-eight million, one hundred eighty-seven thousand, five hundred twenty-one".