28320721 has 8 divisors (see below), whose sum is σ = 33272064. Its totient is φ = 23765520.

The previous prime is 28320713. The next prime is 28320731. The reversal of 28320721 is 12702382.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 28320721 - 2³ = 28320713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28320731) 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 7 ways as a sum of consecutive naturals, for example, 98881 + ... + 99166.

It is an arithmetic number, because the mean of its divisors is an integer number (4159008).

Almost surely, 2^28320721 is an apocalyptic number.

It is an amenable number.

28320721 is a deficient number, since it is larger than the sum of its proper divisors (4951343).

28320721 is a wasteful number, since it uses less digits than its factorization.

28320721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 198071.

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 28320721 is about 5321.7216199271. The cubic root of 28320721 is about 304.8139006263.

The spelling of 28320721 in words is "twenty-eight million, three hundred twenty thousand, seven hundred twenty-one".