28331309 has 4 divisors (see below), whose sum is σ = 28865916. Its totient is φ = 27796704.

The previous prime is 28331291. The next prime is 28331321. The reversal of 28331309 is 90313382.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90313382 = 2 ⋅45156691.

It can be written as a sum of positive squares in 2 ways, for example, as 14478025 + 13853284 = 3805^2 + 3722^2 .

It is a cyclic number.

It is not a de Polignac number, because 28331309 - 2⁸ = 28331053 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28331339) 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, 267224 + ... + 267329.

It is an arithmetic number, because the mean of its divisors is an integer number (7216479).

Almost surely, 2^28331309 is an apocalyptic number.

It is an amenable number.

28331309 is a deficient number, since it is larger than the sum of its proper divisors (534607).

28331309 is an equidigital number, since it uses as much as digits as its factorization.

28331309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 534606.

The product of its (nonzero) digits is 3888, while the sum is 29.

The square root of 28331309 is about 5322.7163178212. The cubic root of 28331309 is about 304.8518818564.

The spelling of 28331309 in words is "twenty-eight million, three hundred thirty-one thousand, three hundred nine".