256500721 has 4 divisors (see below), whose sum is σ = 258898032. Its totient is φ = 254103412.

The previous prime is 256500707. The next prime is 256500733. The reversal of 256500721 is 127005652.

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 256500721 - 2¹¹ = 256498673 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 256500721.

It is not an unprimeable number, because it can be changed into a prime (256500701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1198495 + ... + 1198708.

It is an arithmetic number, because the mean of its divisors is an integer number (64724508).

Almost surely, 2^256500721 is an apocalyptic number.

It is an amenable number.

256500721 is a deficient number, since it is larger than the sum of its proper divisors (2397311).

256500721 is a wasteful number, since it uses less digits than its factorization.

256500721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2397310.

The product of its (nonzero) digits is 4200, while the sum is 28.

The square root of 256500721 is about 16015.6398873102. The cubic root of 256500721 is about 635.3741329649.

The spelling of 256500721 in words is "two hundred fifty-six million, five hundred thousand, seven hundred twenty-one".