256521021 has 4 divisors (see below), whose sum is σ = 342028032. Its totient is φ = 171014012.

The previous prime is 256521019. The next prime is 256521029. The reversal of 256521021 is 120125652.

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 a cyclic number.

It is not a de Polignac number, because 256521021 - 2¹ = 256521019 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 256520982 and 256521000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (256521029) 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, 42753501 + ... + 42753506.

It is an arithmetic number, because the mean of its divisors is an integer number (85507008).

Almost surely, 2^256521021 is an apocalyptic number.

It is an amenable number.

256521021 is a deficient number, since it is larger than the sum of its proper divisors (85507011).

256521021 is an equidigital number, since it uses as much as digits as its factorization.

256521021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85507010.

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 256521021 is about 16016.2736302799. The cubic root of 256521021 is about 635.3908941324.

Adding to 256521021 its reverse (120125652), we get a palindrome (376646673).

The spelling of 256521021 in words is "two hundred fifty-six million, five hundred twenty-one thousand, twenty-one".