256638861 has 24 divisors (see below), whose sum is σ = 385438144. Its totient is φ = 170644320.

The previous prime is 256638841. The next prime is 256638883. The reversal of 256638861 is 168836652.

256638861 is a `hidden beast` number, since 2 + 5 + 6 + 638 + 8 + 6 + 1 = 666.

It is not a de Polignac number, because 256638861 - 2⁵ = 256638829 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256638841) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 109896 + ... + 112206.

Almost surely, 2^256638861 is an apocalyptic number.

It is an amenable number.

256638861 is a deficient number, since it is larger than the sum of its proper divisors (128799283).

256638861 is an equidigital number, since it uses as much as digits as its factorization.

256638861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2783 (or 2771 counting only the distinct ones).

The product of its digits is 414720, while the sum is 45.

The square root of 256638861 is about 16019.9519662201. The cubic root of 256638861 is about 635.4881740102.

The spelling of 256638861 in words is "two hundred fifty-six million, six hundred thirty-eight thousand, eight hundred sixty-one".