28091309 has 4 divisors (see below), whose sum is σ = 28175004. Its totient is φ = 28007616.

The previous prime is 28091279. The next prime is 28091311. The reversal of 28091309 is 90319082.

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 12709225 + 15382084 = 3565^2 + 3922^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28091309 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28091339) 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, 41342 + ... + 42015.

It is an arithmetic number, because the mean of its divisors is an integer number (7043751).

Almost surely, 2^28091309 is an apocalyptic number.

It is an amenable number.

28091309 is a deficient number, since it is larger than the sum of its proper divisors (83695).

28091309 is an equidigital number, since it uses as much as digits as its factorization.

28091309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83694.

The product of its (nonzero) digits is 3888, while the sum is 32.

The square root of 28091309 is about 5300.1234891274. The cubic root of 28091309 is about 303.9886198706.

The spelling of 28091309 in words is "twenty-eight million, ninety-one thousand, three hundred nine".