21928 has 8 divisors (see below), whose sum is σ = 41130. Its totient is φ = 10960.

The previous prime is 21911. The next prime is 21929. The reversal of 21928 is 82912.

It can be written as a sum of positive squares in only one way, i.e., 20164 + 1764 = 142^2 + 42^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a junction number, because it is equal to n+sod(n) for n = 21899 and 21908.

It is not an unprimeable number, because it can be changed into a prime (21929) by changing a digit.

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 as a sum of consecutive naturals, namely, 1363 + ... + 1378.

2²¹⁹²⁸ is an apocalyptic number.

It is an amenable number.

21928 is a deficient number, since it is larger than the sum of its proper divisors (19202).

21928 is a wasteful number, since it uses less digits than its factorization.

21928 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2747 (or 2743 counting only the distinct ones).

The product of its digits is 288, while the sum is 22.

The square root of 21928 is about 148.0810588833. The cubic root of 21928 is about 27.9897921974.

It can be divided in two parts, 21 and 928, that added together give a palindrome (949).

The spelling of 21928 in words is "twenty-one thousand, nine hundred twenty-eight".