28781309 has 4 divisors (see below), whose sum is σ = 28854204. Its totient is φ = 28708416.

The previous prime is 28781297. The next prime is 28781317. The reversal of 28781309 is 90318782.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 90318782 = 2 ⋅45159391.

It can be written as a sum of positive squares in 2 ways, for example, as 14417209 + 14364100 = 3797^2 + 3790^2 .

It is a cyclic number.

It is not a de Polignac number, because 28781309 - 2⁴ = 28781293 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 (28781009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 35852 + ... + 36645.

It is an arithmetic number, because the mean of its divisors is an integer number (7213551).

Almost surely, 2^28781309 is an apocalyptic number.

It is an amenable number.

28781309 is a deficient number, since it is larger than the sum of its proper divisors (72895).

28781309 is an equidigital number, since it uses as much as digits as its factorization.

28781309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72894.

The product of its (nonzero) digits is 24192, while the sum is 38.

The square root of 28781309 is about 5364.8214322566. The cubic root of 28781309 is about 306.4574480072.

The spelling of 28781309 in words is "twenty-eight million, seven hundred eighty-one thousand, three hundred nine".