28015721 has 4 divisors (see below), whose sum is σ = 28399572. Its totient is φ = 27631872.

The previous prime is 28015717. The next prime is 28015777. The reversal of 28015721 is 12751082.

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 18156121 + 9859600 = 4261^2 + 3140^2 .

It is a cyclic number.

It is not a de Polignac number, because 28015721 - 2² = 28015717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28015621) 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, 191816 + ... + 191961.

It is an arithmetic number, because the mean of its divisors is an integer number (7099893).

Almost surely, 2^28015721 is an apocalyptic number.

It is an amenable number.

28015721 is a deficient number, since it is larger than the sum of its proper divisors (383851).

28015721 is an equidigital number, since it uses as much as digits as its factorization.

28015721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 383850.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 28015721 is about 5292.9879085447. The cubic root of 28015721 is about 303.7157177633.

The spelling of 28015721 in words is "twenty-eight million, fifteen thousand, seven hundred twenty-one".