256721865 has 8 divisors (see below), whose sum is σ = 410755008. Its totient is φ = 136918320.

The previous prime is 256721827. The next prime is 256721867. The reversal of 256721865 is 568127652.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 256721865 - 2⁸ = 256721609 is a prime.

It is a super-2 number, since 2×256721865² = 131812231938156450, 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 in 7 ways as a sum of consecutive naturals, for example, 8557381 + ... + 8557410.

It is an arithmetic number, because the mean of its divisors is an integer number (51344376).

Almost surely, 2^256721865 is an apocalyptic number.

It is an amenable number.

256721865 is a deficient number, since it is larger than the sum of its proper divisors (154033143).

256721865 is a wasteful number, since it uses less digits than its factorization.

256721865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17114799.

The product of its digits is 201600, while the sum is 42.

The square root of 256721865 is about 16022.5424012546. The cubic root of 256721865 is about 635.5566780220.

The spelling of 256721865 in words is "two hundred fifty-six million, seven hundred twenty-one thousand, eight hundred sixty-five".