28371821 has 4 divisors (see below), whose sum is σ = 28664412. Its totient is φ = 28079232.

The previous prime is 28371781. The next prime is 28371829. The reversal of 28371821 is 12817382.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12817382 = 2 ⋅6408691.

It can be written as a sum of positive squares in 2 ways, for example, as 10824100 + 17547721 = 3290^2 + 4189^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-28371821 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28371829) 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, 146150 + ... + 146343.

It is an arithmetic number, because the mean of its divisors is an integer number (7166103).

Almost surely, 2^28371821 is an apocalyptic number.

It is an amenable number.

28371821 is a deficient number, since it is larger than the sum of its proper divisors (292591).

28371821 is an equidigital number, since it uses as much as digits as its factorization.

28371821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 292590.

The product of its digits is 5376, while the sum is 32.

The square root of 28371821 is about 5326.5205340823. The cubic root of 28371821 is about 304.9971190268.

It can be divided in two parts, 28371 and 821, that added together give a palindrome (29192).

The spelling of 28371821 in words is "twenty-eight million, three hundred seventy-one thousand, eight hundred twenty-one".