25001556561 has 12 divisors (see below), whose sum is σ = 36204330292. Its totient is φ = 16625717856.

The previous prime is 25001556557. The next prime is 25001556649. The reversal of 25001556561 is 16565510052.

25001556561 is a `hidden beast` number, since 2 + 50 + 0 + 1 + 556 + 56 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 11309046336 + 13692510225 = 106344^2 + 117015^2 .

It is not a de Polignac number, because 25001556561 - 2² = 25001556557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (25001556551) 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, 3495106 + ... + 3502251.

Almost surely, 2^25001556561 is an apocalyptic number.

It is an amenable number.

25001556561 is a deficient number, since it is larger than the sum of its proper divisors (11202773731).

25001556561 is a wasteful number, since it uses less digits than its factorization.

25001556561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6997760 (or 6997757 counting only the distinct ones).

The product of its (nonzero) digits is 45000, while the sum is 36.

The spelling of 25001556561 in words is "twenty-five billion, one million, five hundred fifty-six thousand, five hundred sixty-one".