28118721 has 4 divisors (see below), whose sum is σ = 37491632. Its totient is φ = 18745812.

The previous prime is 28118693. The next prime is 28118729. The reversal of 28118721 is 12781182.

It is a happy number.

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 28118721 - 2⁷ = 28118593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28118729) 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, 4686451 + ... + 4686456.

It is an arithmetic number, because the mean of its divisors is an integer number (9372908).

Almost surely, 2^28118721 is an apocalyptic number.

It is an amenable number.

28118721 is a deficient number, since it is larger than the sum of its proper divisors (9372911).

28118721 is an equidigital number, since it uses as much as digits as its factorization.

28118721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9372910.

The product of its digits is 1792, while the sum is 30.

The square root of 28118721 is about 5302.7088360573. The cubic root of 28118721 is about 304.0874668965.

The spelling of 28118721 in words is "twenty-eight million, one hundred eighteen thousand, seven hundred twenty-one".