21533 has 4 divisors (see below), whose sum is σ = 21948. Its totient is φ = 21120.

The previous prime is 21529. The next prime is 21557. The reversal of 21533 is 33512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3844 + 17689 = 62^2 + 133^2 .

It is a cyclic number.

It is not a de Polignac number, because 21533 - 2² = 21529 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21503) 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 in 3 ways as a sum of consecutive naturals, for example, 116 + ... + 237.

It is an arithmetic number, because the mean of its divisors is an integer number (5487).

2²¹⁵³³ is an apocalyptic number.

It is an amenable number.

21533 is a deficient number, since it is larger than the sum of its proper divisors (415).

21533 is an equidigital number, since it uses as much as digits as its factorization.

21533 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 414.

The product of its digits is 90, while the sum is 14.

The square root of 21533 is about 146.7412689055. The cubic root of 21533 is about 27.8207081358.

The spelling of 21533 in words is "twenty-one thousand, five hundred thirty-three".