256721866 has 4 divisors (see below), whose sum is σ = 385082802. Its totient is φ = 128360932.

The previous prime is 256721827. The next prime is 256721867. The reversal of 256721866 is 668127652.

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

It can be written as a sum of positive squares in only one way, i.e., 211091841 + 45630025 = 14529^2 + 6755^2 .

It is a super-2 number, since 2×256721866² = 131812232965043912, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (256721867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64180465 + ... + 64180468.

Almost surely, 2^256721866 is an apocalyptic number.

256721866 is a deficient number, since it is larger than the sum of its proper divisors (128360936).

256721866 is a wasteful number, since it uses less digits than its factorization.

256721866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128360935.

The product of its digits is 241920, while the sum is 43.

The square root of 256721866 is about 16022.5424324606. The cubic root of 256721866 is about 635.5566788472.

The spelling of 256721866 in words is "two hundred fifty-six million, seven hundred twenty-one thousand, eight hundred sixty-six".