28648721 has 4 divisors (see below), whose sum is σ = 28664244. Its totient is φ = 28633200.

The previous prime is 28648703. The next prime is 28648733. The reversal of 28648721 is 12784682.

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 16321600 + 12327121 = 4040^2 + 3511^2 .

It is a cyclic number.

It is not a de Polignac number, because 28648721 - 2⁶ = 28648657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28642721) 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 3 ways as a sum of consecutive naturals, for example, 4550 + ... + 8831.

It is an arithmetic number, because the mean of its divisors is an integer number (7166061).

Almost surely, 2^28648721 is an apocalyptic number.

It is an amenable number.

28648721 is a deficient number, since it is larger than the sum of its proper divisors (15523).

28648721 is a wasteful number, since it uses less digits than its factorization.

28648721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15522.

The product of its digits is 43008, while the sum is 38.

The square root of 28648721 is about 5352.4499997665. The cubic root of 28648721 is about 305.9861336220.

The spelling of 28648721 in words is "twenty-eight million, six hundred forty-eight thousand, seven hundred twenty-one".