256776721 has 4 divisors (see below), whose sum is σ = 271881252. Its totient is φ = 241672192.

The previous prime is 256776713. The next prime is 256776733. The reversal of 256776721 is 127677652.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 100801600 + 155975121 = 10040^2 + 12489^2 .

It is a cyclic number.

It is not a de Polignac number, because 256776721 - 2³ = 256776713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256770721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7552240 + ... + 7552273.

It is an arithmetic number, because the mean of its divisors is an integer number (67970313).

Almost surely, 2^256776721 is an apocalyptic number.

It is an amenable number.

256776721 is a deficient number, since it is larger than the sum of its proper divisors (15104531).

256776721 is a wasteful number, since it uses less digits than its factorization.

256776721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15104530.

The product of its digits is 246960, while the sum is 43.

The square root of 256776721 is about 16024.2541480095. The cubic root of 256776721 is about 635.6019431110.

The spelling of 256776721 in words is "two hundred fifty-six million, seven hundred seventy-six thousand, seven hundred twenty-one".