21525 has 24 divisors (see below), whose sum is σ = 41664. Its totient is φ = 9600.

The previous prime is 21523. The next prime is 21529. The reversal of 21525 is 52512.

21525 is nontrivially palindromic in base 2, base 4, base 8 and base 14.

It is not a de Polignac number, because 21525 - 2¹ = 21523 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a Curzon number.

It is a zygodrome in base 4.

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 polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 505 + ... + 545.

It is an arithmetic number, because the mean of its divisors is an integer number (1736).

2²¹⁵²⁵ is an apocalyptic number.

21525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21525 is a deficient number, since it is larger than the sum of its proper divisors (20139).

21525 is a wasteful number, since it uses less digits than its factorization.

21525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61 (or 56 counting only the distinct ones).

The product of its digits is 100, while the sum is 15.

The square root of 21525 is about 146.7140075112. The cubic root of 21525 is about 27.8172623667.

It can be divided in two parts, 21 and 525, that multiplied together give a square (11025 = 105²).

The spelling of 21525 in words is "twenty-one thousand, five hundred twenty-five".