256975781 has 2 divisors, whose sum is σ = 256975782. Its totient is φ = 256975780.

The previous prime is 256975769. The next prime is 256975799. The reversal of 256975781 is 187579652.

256975781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 255040900 + 1934881 = 15970^2 + 1391^2 .

It is a cyclic number.

It is not a de Polignac number, because 256975781 - 2¹⁴ = 256959397 is a prime.

It is a super-2 number, since 2×256975781² = 132073104041119922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (255975781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128487890 + 128487891.

It is an arithmetic number, because the mean of its divisors is an integer number (128487891).

Almost surely, 2^256975781 is an apocalyptic number.

It is an amenable number.

256975781 is a deficient number, since it is larger than the sum of its proper divisors (1).

256975781 is an equidigital number, since it uses as much as digits as its factorization.

256975781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1058400, while the sum is 50.

The square root of 256975781 is about 16030.4641542283. The cubic root of 256975781 is about 635.7661457455.

The spelling of 256975781 in words is "two hundred fifty-six million, nine hundred seventy-five thousand, seven hundred eighty-one".