256405999 has 2 divisors, whose sum is σ = 256406000. Its totient is φ = 256405998.

The previous prime is 256405979. The next prime is 256406011. The reversal of 256405999 is 999504652.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 256405999 - 2⁷ = 256405871 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (256405939) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128202999 + 128203000.

It is an arithmetic number, because the mean of its divisors is an integer number (128203000).

Almost surely, 2^256405999 is an apocalyptic number.

256405999 is a deficient number, since it is larger than the sum of its proper divisors (1).

256405999 is an equidigital number, since it uses as much as digits as its factorization.

256405999 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 874800, while the sum is 49.

The square root of 256405999 is about 16012.6824423642. The cubic root of 256405999 is about 635.2959118482.

The spelling of 256405999 in words is "two hundred fifty-six million, four hundred five thousand, nine hundred ninety-nine".