21524 has 6 divisors (see below), whose sum is σ = 37674. Its totient is φ = 10760.

The previous prime is 21523. The next prime is 21529. The reversal of 21524 is 42512.

It can be written as a sum of positive squares in only one way, i.e., 16900 + 4624 = 130^2 + 68^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21499 and 21508.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521) 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 as a sum of consecutive naturals, namely, 2687 + ... + 2694.

It is an arithmetic number, because the mean of its divisors is an integer number (6279).

2²¹⁵²⁴ is an apocalyptic number.

It is an amenable number.

21524 is a deficient number, since it is larger than the sum of its proper divisors (16150).

21524 is a wasteful number, since it uses less digits than its factorization.

21524 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5385 (or 5383 counting only the distinct ones).

The product of its digits is 80, while the sum is 14.

The square root of 21524 is about 146.7105994807. The cubic root of 21524 is about 27.8168315856.

It can be divided in two parts, 21 and 524, that added together give a palindrome (545).

The spelling of 21524 in words is "twenty-one thousand, five hundred twenty-four".