28728781 has 8 divisors (see below), whose sum is σ = 29292984. Its totient is φ = 28170240.

The previous prime is 28728769. The next prime is 28728787. The reversal of 28728781 is 18782782.

It can be written as a sum of positive squares in 4 ways, for example, as 1334025 + 27394756 = 1155^2 + 5234^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 28728781 - 2⁹ = 28728269 is a prime.

It is a super-2 number, since 2×28728781² = 1650685715491922, which contains 22 as substring.

It is a Duffinian number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28728787) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9651 + ... + 12271.

It is an arithmetic number, because the mean of its divisors is an integer number (3661623).

Almost surely, 2^28728781 is an apocalyptic number.

It is an amenable number.

28728781 is a deficient number, since it is larger than the sum of its proper divisors (564203).

28728781 is a wasteful number, since it uses less digits than its factorization.

28728781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2831.

The product of its digits is 100352, while the sum is 43.

The square root of 28728781 is about 5359.9236002018. The cubic root of 28728781 is about 306.2708986988.

The spelling of 28728781 in words is "twenty-eight million, seven hundred twenty-eight thousand, seven hundred eighty-one".