28748721 has 4 divisors (see below), whose sum is σ = 38331632. Its totient is φ = 19165812.

The previous prime is 28748719. The next prime is 28748743. The reversal of 28748721 is 12784782.

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 not a de Polignac number, because 28748721 - 2¹ = 28748719 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 28748721.

It is not an unprimeable number, because it can be changed into a prime (28748761) 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, 4791451 + ... + 4791456.

It is an arithmetic number, because the mean of its divisors is an integer number (9582908).

Almost surely, 2^28748721 is an apocalyptic number.

It is an amenable number.

28748721 is a deficient number, since it is larger than the sum of its proper divisors (9582911).

28748721 is an equidigital number, since it uses as much as digits as its factorization.

28748721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9582910.

The product of its digits is 50176, while the sum is 39.

The square root of 28748721 is about 5361.7833786903. The cubic root of 28748721 is about 306.3417408895.

The spelling of 28748721 in words is "twenty-eight million, seven hundred forty-eight thousand, seven hundred twenty-one".