256867721 has 4 divisors (see below), whose sum is σ = 280219344. Its totient is φ = 233516100.

The previous prime is 256867717. The next prime is 256867729. The reversal of 256867721 is 127768652.

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 256867721 - 2² = 256867717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (256867729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11675795 + ... + 11675816.

It is an arithmetic number, because the mean of its divisors is an integer number (70054836).

Almost surely, 2^256867721 is an apocalyptic number.

It is an amenable number.

256867721 is a deficient number, since it is larger than the sum of its proper divisors (23351623).

256867721 is a wasteful number, since it uses less digits than its factorization.

256867721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23351622.

The product of its digits is 282240, while the sum is 44.

The square root of 256867721 is about 16027.0933422127. The cubic root of 256867721 is about 635.6770186413.

The spelling of 256867721 in words is "two hundred fifty-six million, eight hundred sixty-seven thousand, seven hundred twenty-one".