28181821 has 4 divisors (see below), whose sum is σ = 29090944. Its totient is φ = 27272700.

The previous prime is 28181809. The next prime is 28181837. The reversal of 28181821 is 12818182.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 28181821 - 2⁵ = 28181789 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 909091 = 28181821 / (2 + 8 + 1 + 8 + 1 + 8 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28181851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 454515 + ... + 454576.

It is an arithmetic number, because the mean of its divisors is an integer number (7272736).

Almost surely, 2^28181821 is an apocalyptic number.

It is an amenable number.

28181821 is a deficient number, since it is larger than the sum of its proper divisors (909123).

28181821 is an equidigital number, since it uses as much as digits as its factorization.

28181821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 909122.

The product of its digits is 2048, while the sum is 31.

The square root of 28181821 is about 5308.6552911260. The cubic root of 28181821 is about 304.3147601187.

The spelling of 28181821 in words is "twenty-eight million, one hundred eighty-one thousand, eight hundred twenty-one".