28240 has 20 divisors (see below), whose sum is σ = 65844. Its totient is φ = 11264.

The previous prime is 28229. The next prime is 28277. The reversal of 28240 is 4282.

It can be written as a sum of positive squares in 2 ways, for example, as 10816 + 17424 = 104^2 + 132^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 97 + ... + 256.

2²⁸²⁴⁰ is an apocalyptic number.

28240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

28240 is an abundant number, since it is smaller than the sum of its proper divisors (37604).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32922).

28240 is a wasteful number, since it uses less digits than its factorization.

28240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366 (or 360 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 16.

The square root of 28240 is about 168.0476123008. The cubic root of 28240 is about 30.4524026926.

Subtracting from 28240 its sum of digits (16), we obtain a square (28224 = 168²).

The spelling of 28240 in words is "twenty-eight thousand, two hundred forty".