25561 has 2 divisors, whose sum is σ = 25562. Its totient is φ = 25560.

The previous prime is 25541. The next prime is 25577. The reversal of 25561 is 16552.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 24336 + 1225 = 156^2 + 35^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-25561 is a prime.

It is a Chen prime.

25561 is a lucky number.

It is a nialpdrome in base 13.

It is not a weakly prime, because it can be changed into another prime (25541) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 12780 + 12781.

It is an arithmetic number, because the mean of its divisors is an integer number (12781).

2²⁵⁵⁶¹ is an apocalyptic number.

25561 is the 72-nd centered decagonal number.

It is an amenable number.

25561 is a deficient number, since it is larger than the sum of its proper divisors (1).

25561 is an equidigital number, since it uses as much as digits as its factorization.

25561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 300, while the sum is 19.

The square root of 25561 is about 159.8780785474. The cubic root of 25561 is about 29.4572780046.

Subtracting from 25561 its reverse (16552), we obtain a palindrome (9009).

The spelling of 25561 in words is "twenty-five thousand, five hundred sixty-one".