21528 has 48 divisors (see below), whose sum is σ = 65520. Its totient is φ = 6336.

The previous prime is 21523. The next prime is 21529. The reversal of 21528 is 82512.

21528 = T₂₇ + T₂₈ + ... + T₅₂.

21528 is a nontrivial binomial coefficient, being equal to C(208, 2).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a self number, because there is not a number n which added to its sum of digits gives 21528.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521) by changing a digit.

21528 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 11 ways as a sum of consecutive naturals, for example, 925 + ... + 947.

It is an arithmetic number, because the mean of its divisors is an integer number (1365).

2²¹⁵²⁸ is an apocalyptic number.

21528 is the 207-th triangular number and also the 104-th hexagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21528, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32760).

21528 is an abundant number, since it is smaller than the sum of its proper divisors (43992).

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

21528 is a wasteful number, since it uses less digits than its factorization.

21528 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48 (or 41 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21528 is about 146.7242311276. The cubic root of 21528 is about 27.8185546302.

It can be divided in two parts, 215 and 28, that added together give a 5-th power (243 = 3⁵).

The spelling of 21528 in words is "twenty-one thousand, five hundred twenty-eight".