28728181 has 4 divisors (see below), whose sum is σ = 30418092. Its totient is φ = 27038272.

The previous prime is 28728163. The next prime is 28728191. The reversal of 28728181 is 18182782.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18182782 = 2 ⋅9091391.

It can be written as a sum of positive squares in 2 ways, for example, as 9979281 + 18748900 = 3159^2 + 4330^2 .

It is a cyclic number.

It is not a de Polignac number, because 28728181 - 2¹³ = 28719989 is a prime.

It is a super-2 number, since 2×28728181² = 1650616767137522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 28728181.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28728121) 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, 844930 + ... + 844963.

It is an arithmetic number, because the mean of its divisors is an integer number (7604523).

Almost surely, 2^28728181 is an apocalyptic number.

It is an amenable number.

28728181 is a deficient number, since it is larger than the sum of its proper divisors (1689911).

28728181 is a wasteful number, since it uses less digits than its factorization.

28728181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1689910.

The product of its digits is 14336, while the sum is 37.

The square root of 28728181 is about 5359.8676289625. The cubic root of 28728181 is about 306.2687665301.

The spelling of 28728181 in words is "twenty-eight million, seven hundred twenty-eight thousand, one hundred eighty-one".