256605561 has 6 divisors (see below), whose sum is σ = 370652490. Its totient is φ = 171070368.

The previous prime is 256605533. The next prime is 256605563. The reversal of 256605561 is 165506652.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 247873536 + 8732025 = 15744^2 + 2955^2 .

It is not a de Polignac number, because 256605561 - 2⁹ = 256605049 is a prime.

It is a super-2 number, since 2×256605561² = 131692827872249442, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (256605563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 14255856 + ... + 14255873.

It is an arithmetic number, because the mean of its divisors is an integer number (61775415).

Almost surely, 2^256605561 is an apocalyptic number.

It is an amenable number.

256605561 is a deficient number, since it is larger than the sum of its proper divisors (114046929).

256605561 is a wasteful number, since it uses less digits than its factorization.

256605561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28511735 (or 28511732 counting only the distinct ones).

The product of its (nonzero) digits is 54000, while the sum is 36.

The square root of 256605561 is about 16018.9126035446. The cubic root of 256605561 is about 635.4606870434.

The spelling of 256605561 in words is "two hundred fifty-six million, six hundred five thousand, five hundred sixty-one".