28721305 has 4 divisors (see below), whose sum is σ = 34465572. Its totient is φ = 22977040.

The previous prime is 28721267. The next prime is 28721309. The reversal of 28721305 is 50312782.

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 14220441 + 14500864 = 3771^2 + 3808^2 .

It is a de Polignac number, because none of the positive numbers 2^k-28721305 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28721309) 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, 2872126 + ... + 2872135.

It is an arithmetic number, because the mean of its divisors is an integer number (8616393).

Almost surely, 2^28721305 is an apocalyptic number.

It is an amenable number.

28721305 is a deficient number, since it is larger than the sum of its proper divisors (5744267).

28721305 is an equidigital number, since it uses as much as digits as its factorization.

28721305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5744266.

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 28721305 is about 5359.2261568253. The cubic root of 28721305 is about 306.2443297576.

The spelling of 28721305 in words is "twenty-eight million, seven hundred twenty-one thousand, three hundred five".