256021009 has 2 divisors, whose sum is σ = 256021010. Its totient is φ = 256021008.

The previous prime is 256020967. The next prime is 256021021. The reversal of 256021009 is 900120652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 251920384 + 4100625 = 15872^2 + 2025^2 .

It is a cyclic number.

It is not a de Polignac number, because 256021009 - 2⁷ = 256020881 is a prime.

It is not a weakly prime, because it can be changed into another prime (256021039) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128010504 + 128010505.

It is an arithmetic number, because the mean of its divisors is an integer number (128010505).

Almost surely, 2^256021009 is an apocalyptic number.

It is an amenable number.

256021009 is a deficient number, since it is larger than the sum of its proper divisors (1).

256021009 is an equidigital number, since it uses as much as digits as its factorization.

256021009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 256021009 is about 16000.6565177808. The cubic root of 256021009 is about 634.9777899521.

The spelling of 256021009 in words is "two hundred fifty-six million, twenty-one thousand, nine".