25821 has 12 divisors (see below), whose sum is σ = 39520. Its totient is φ = 16200.

The previous prime is 25819. The next prime is 25841. The reversal of 25821 is 12852.

It is not a de Polignac number, because 25821 - 2¹ = 25819 is a prime.

25821 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 25794 and 25803.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (25801) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 96 + ... + 246.

2²⁵⁸²¹ is an apocalyptic number.

It is an amenable number.

25821 is a deficient number, since it is larger than the sum of its proper divisors (13699).

25821 is a wasteful number, since it uses less digits than its factorization.

25821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176 (or 173 counting only the distinct ones).

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

The square root of 25821 is about 160.6891408901. The cubic root of 25821 is about 29.5568185799.

The spelling of 25821 in words is "twenty-five thousand, eight hundred twenty-one".