256505817 has 4 divisors (see below), whose sum is σ = 342007760. Its totient is φ = 171003876.

The previous prime is 256505813. The next prime is 256505827. The reversal of 256505817 is 718505652.

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 not a de Polignac number, because 256505817 - 2² = 256505813 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256505813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 42750967 + ... + 42750972.

It is an arithmetic number, because the mean of its divisors is an integer number (85501940).

Almost surely, 2^256505817 is an apocalyptic number.

It is an amenable number.

256505817 is a deficient number, since it is larger than the sum of its proper divisors (85501943).

256505817 is an equidigital number, since it uses as much as digits as its factorization.

256505817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85501942.

The product of its (nonzero) digits is 84000, while the sum is 39.

The square root of 256505817 is about 16015.7989810062. The cubic root of 256505817 is about 635.3783406791.

The spelling of 256505817 in words is "two hundred fifty-six million, five hundred five thousand, eight hundred seventeen".