256781 has 4 divisors (see below), whose sum is σ = 293472. Its totient is φ = 220092.

The previous prime is 256771. The next prime is 256799. The reversal of 256781 is 187652.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 256781 - 2¹⁰ = 255757 is a prime.

It is a super-2 number, since 2×256781² = 131872963922, which contains 22 as substring.

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

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 256781.

It is not an unprimeable number, because it can be changed into a prime (256721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18335 + ... + 18348.

It is an arithmetic number, because the mean of its divisors is an integer number (73368).

2²⁵⁶⁷⁸¹ is an apocalyptic number.

It is an amenable number.

256781 is a deficient number, since it is larger than the sum of its proper divisors (36691).

256781 is an equidigital number, since it uses as much as digits as its factorization.

256781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36690.

The product of its digits is 3360, while the sum is 29.

The square root of 256781 is about 506.7356312714. The cubic root of 256781 is about 63.5605473708.

The spelling of 256781 in words is "two hundred fifty-six thousand, seven hundred eighty-one".