21128 has 16 divisors (see below), whose sum is σ = 42000. Its totient is φ = 9936.

The previous prime is 21121. The next prime is 21139. The reversal of 21128 is 82112.

It is a nude number because it is divisible by every one of its digits.

It is not an unprimeable number, because it can be changed into a prime (21121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 83 + ... + 221.

It is an arithmetic number, because the mean of its divisors is an integer number (2625).

2²¹¹²⁸ is an apocalyptic number.

It is an amenable number.

21128 is a deficient number, since it is larger than the sum of its proper divisors (20872).

21128 is a wasteful number, since it uses less digits than its factorization.

21128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 164 (or 160 counting only the distinct ones).

The product of its digits is 32, while the sum is 14.

The square root of 21128 is about 145.3547384849. The cubic root of 21128 is about 27.6451825922.

The spelling of 21128 in words is "twenty-one thousand, one hundred twenty-eight".