28028721 has 16 divisors (see below), whose sum is σ = 43865984. Its totient is φ = 15583104.

The previous prime is 28028701. The next prime is 28028723. The reversal of 28028721 is 12782082.

It is a happy number.

It is not a de Polignac number, because 28028721 - 2⁶ = 28028657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28028723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17260 + ... + 18813.

It is an arithmetic number, because the mean of its divisors is an integer number (2741624).

Almost surely, 2^28028721 is an apocalyptic number.

28028721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

28028721 is a deficient number, since it is larger than the sum of its proper divisors (15837263).

28028721 is a wasteful number, since it uses less digits than its factorization.

28028721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36120.

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 28028721 is about 5294.2158059528. The cubic root of 28028721 is about 303.7626877459.

The spelling of 28028721 in words is "twenty-eight million, twenty-eight thousand, seven hundred twenty-one".