256581 has 32 divisors (see below), whose sum is σ = 443520. Its totient is φ = 145152.

The previous prime is 256579. The next prime is 256589. The reversal of 256581 is 185652.

256581 is a `hidden beast` number, since 2 + 5 + 658 + 1 = 666.

It is not a de Polignac number, because 256581 - 2¹ = 256579 is a prime.

It is a super-2 number, since 2×256581² = 131667619122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an alternating number because its digits alternate between even and odd.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256589) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5946 + ... + 5988.

It is an arithmetic number, because the mean of its divisors is an integer number (13860).

2²⁵⁶⁵⁸¹ is an apocalyptic number.

It is an amenable number.

256581 is a deficient number, since it is larger than the sum of its proper divisors (186939).

256581 is a wasteful number, since it uses less digits than its factorization.

256581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82 (or 76 counting only the distinct ones).

The product of its digits is 2400, while the sum is 27.

The square root of 256581 is about 506.5382512703. The cubic root of 256581 is about 63.5440412024.

The spelling of 256581 in words is "two hundred fifty-six thousand, five hundred eighty-one".