256000021 has 4 divisors (see below), whose sum is σ = 256428000. Its totient is φ = 255572044.

The previous prime is 256000009. The next prime is 256000033. The reversal of 256000021 is 120000652.

It is a happy number.

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 an interprime number because it is at equal distance from previous prime (256000009) and next prime (256000033).

It is a cyclic number.

It is not a de Polignac number, because 256000021 - 2⁹ = 255999509 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 255999959 and 256000004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256000001) 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, 213091 + ... + 214288.

It is an arithmetic number, because the mean of its divisors is an integer number (64107000).

Almost surely, 2^256000021 is an apocalyptic number.

It is an amenable number.

256000021 is a deficient number, since it is larger than the sum of its proper divisors (427979).

256000021 is an equidigital number, since it uses as much as digits as its factorization.

256000021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 427978.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 256000021 is about 16000.0006562500. Note that the first 3 decimals coincide. The cubic root of 256000021 is about 634.9604381495.

Adding to 256000021 its reverse (120000652), we get a palindrome (376000673).

The spelling of 256000021 in words is "two hundred fifty-six million, twenty-one", and thus it is an aban number.