25661561 has 2 divisors, whose sum is σ = 25661562. Its totient is φ = 25661560.

The previous prime is 25661527. The next prime is 25661563. The reversal of 25661561 is 16516652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21335161 + 4326400 = 4619^2 + 2080^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-25661561 is a prime.

Together with 25661563, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (25661563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 12830780 + 12830781.

It is an arithmetic number, because the mean of its divisors is an integer number (12830781).

Almost surely, 2^25661561 is an apocalyptic number.

It is an amenable number.

25661561 is a deficient number, since it is larger than the sum of its proper divisors (1).

25661561 is an equidigital number, since it uses as much as digits as its factorization.

25661561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10800, while the sum is 32.

The square root of 25661561 is about 5065.7241338233. The cubic root of 25661561 is about 294.9585731351.

The spelling of 25661561 in words is "twenty-five million, six hundred sixty-one thousand, five hundred sixty-one".