21825 has 18 divisors (see below), whose sum is σ = 39494. Its totient is φ = 11520.

The previous prime is 21821. The next prime is 21839. The reversal of 21825 is 52812.

21825 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 3 ways, for example, as 1089 + 20736 = 33^2 + 144^2 .

It is not a de Polignac number, because 21825 - 2² = 21821 is a prime.

It is a Duffinian number.

21825 is strictly pandigital in base 6.

It is a Curzon number.

It is a nialpdrome in base 16.

It is a junction number, because it is equal to n+sod(n) for n = 21798 and 21807.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21825.

It is not an unprimeable number, because it can be changed into a prime (21821) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 177 + ... + 273.

2²¹⁸²⁵ is an apocalyptic number.

21825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21825 is a deficient number, since it is larger than the sum of its proper divisors (17669).

21825 is a wasteful number, since it uses less digits than its factorization.

21825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 113 (or 105 counting only the distinct ones).

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

The square root of 21825 is about 147.7328670269. The cubic root of 21825 is about 27.9458989356.

It can be divided in two parts, 2182 and 5, that added together give a 7-th power (2187 = 3⁷).

The spelling of 21825 in words is "twenty-one thousand, eight hundred twenty-five".