25661 has 4 divisors (see below), whose sum is σ = 26112. Its totient is φ = 25212.

The previous prime is 25657. The next prime is 25667. The reversal of 25661 is 16652.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 25661 - 2² = 25657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (25667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 125 + ... + 258.

It is an arithmetic number, because the mean of its divisors is an integer number (6528).

2²⁵⁶⁶¹ is an apocalyptic number.

It is an amenable number.

25661 is a deficient number, since it is larger than the sum of its proper divisors (451).

25661 is an equidigital number, since it uses as much as digits as its factorization.

25661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 450.

The product of its digits is 360, while the sum is 20.

The square root of 25661 is about 160.1905115792. The cubic root of 25661 is about 29.4956423708.

Subtracting from 25661 its reverse (16652), we obtain a palindrome (9009).

It can be divided in two parts, 25 and 661, that added together give a palindrome (686).

The spelling of 25661 in words is "twenty-five thousand, six hundred sixty-one".