256721867 has 2 divisors, whose sum is σ = 256721868. Its totient is φ = 256721866.

The previous prime is 256721827. The next prime is 256721887. The reversal of 256721867 is 768127652.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 256721867 - 2¹⁰ = 256720843 is a prime.

It is a super-2 number, since 2×256721867² = 131812233991931378, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (256721827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128360933 + 128360934.

It is an arithmetic number, because the mean of its divisors is an integer number (128360934).

Almost surely, 2^256721867 is an apocalyptic number.

256721867 is a deficient number, since it is larger than the sum of its proper divisors (1).

256721867 is an equidigital number, since it uses as much as digits as its factorization.

256721867 is an evil number, because the sum of its binary digits is even.

The product of its digits is 282240, while the sum is 44.

The square root of 256721867 is about 16022.5424636666. The cubic root of 256721867 is about 635.5566796724.

The spelling of 256721867 in words is "two hundred fifty-six million, seven hundred twenty-one thousand, eight hundred sixty-seven".