28720809 has 12 divisors (see below), whose sum is σ = 44676996. Its totient is φ = 17674272.

The previous prime is 28720801. The next prime is 28720819. The reversal of 28720809 is 90802782.

It can be written as a sum of positive squares in 2 ways, for example, as 6110784 + 22610025 = 2472^2 + 4755^2 .

It is not a de Polignac number, because 28720809 - 2³ = 28720801 is a prime.

It is a super-2 number, since 2×28720809² = 1649769739228962, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (28720801) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 122622 + ... + 122855.

It is an arithmetic number, because the mean of its divisors is an integer number (3723083).

Almost surely, 2^28720809 is an apocalyptic number.

It is an amenable number.

28720809 is a deficient number, since it is larger than the sum of its proper divisors (15956187).

28720809 is a wasteful number, since it uses less digits than its factorization.

28720809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 245496 (or 245493 counting only the distinct ones).

The product of its (nonzero) digits is 16128, while the sum is 36.

The square root of 28720809 is about 5359.1798812878. The cubic root of 28720809 is about 306.2425668611.

The spelling of 28720809 in words is "twenty-eight million, seven hundred twenty thousand, eight hundred nine".