28500781 has 4 divisors (see below), whose sum is σ = 29195964. Its totient is φ = 27805600.

The previous prime is 28500763. The next prime is 28500827. The reversal of 28500781 is 18700582.

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 14699556 + 13801225 = 3834^2 + 3715^2 .

It is a cyclic number.

It is not a de Polignac number, because 28500781 - 2¹¹ = 28498733 is a prime.

It is a super-2 number, since 2×28500781² = 1624589035219922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28504781) 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, 347530 + ... + 347611.

It is an arithmetic number, because the mean of its divisors is an integer number (7298991).

Almost surely, 2^28500781 is an apocalyptic number.

28500781 is the 2388-th centered decagonal number.

It is an amenable number.

28500781 is a deficient number, since it is larger than the sum of its proper divisors (695183).

28500781 is an equidigital number, since it uses as much as digits as its factorization.

28500781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 695182.

The product of its (nonzero) digits is 4480, while the sum is 31.

The square root of 28500781 is about 5338.6122728664. The cubic root of 28500781 is about 305.4585273753.

The spelling of 28500781 in words is "twenty-eight million, five hundred thousand, seven hundred eighty-one".