28508721 has 8 divisors (see below), whose sum is σ = 40012320. Its totient is φ = 18005472.

The previous prime is 28508713. The next prime is 28508723. The reversal of 28508721 is 12780582.

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

It is not a de Polignac number, because 28508721 - 2³ = 28508713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (28508723) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 250020 + ... + 250133.

It is an arithmetic number, because the mean of its divisors is an integer number (5001540).

Almost surely, 2^28508721 is an apocalyptic number.

It is an amenable number.

28508721 is a deficient number, since it is larger than the sum of its proper divisors (11503599).

28508721 is a wasteful number, since it uses less digits than its factorization.

28508721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 500175.

The product of its (nonzero) digits is 8960, while the sum is 33.

The square root of 28508721 is about 5339.3558600266. The cubic root of 28508721 is about 305.4868905223.

The spelling of 28508721 in words is "twenty-eight million, five hundred eight thousand, seven hundred twenty-one".