25666561 has 4 divisors (see below), whose sum is σ = 26049712. Its totient is φ = 25283412.

The previous prime is 25666477. The next prime is 25666577. The reversal of 25666561 is 16566652.

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 25666561 - 2²¹ = 23569409 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 25666561.

It is not an unprimeable number, because it can be changed into a prime (25666661) 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, 191475 + ... + 191608.

It is an arithmetic number, because the mean of its divisors is an integer number (6512428).

Almost surely, 2^25666561 is an apocalyptic number.

It is an amenable number.

25666561 is a deficient number, since it is larger than the sum of its proper divisors (383151).

25666561 is an equidigital number, since it uses as much as digits as its factorization.

25666561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 383150.

The product of its digits is 64800, while the sum is 37.

The square root of 25666561 is about 5066.2176226451. The cubic root of 25666561 is about 294.9777288559.

Subtracting from 25666561 its reverse (16566652), we obtain a palindrome (9099909).

The spelling of 25666561 in words is "twenty-five million, six hundred sixty-six thousand, five hundred sixty-one".