256391 has 2 divisors, whose sum is σ = 256392. Its totient is φ = 256390.
The previous prime is 256369. The next prime is 256393. The reversal of 256391 is 193652.
It is a strong prime.
It is a cyclic number.
It is not a de Polignac number, because 256391 - 214 = 240007 is a prime.
Together with 256393, it forms a pair of twin primes.
It is a Chen prime.
It is a self number, because there is not a number n which added to its sum of digits gives 256391.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 256391.
It is not a weakly prime, because it can be changed into another prime (256393) 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, 128195 + 128196.
It is an arithmetic number, because the mean of its divisors is an integer number (128196).
2256391 is an apocalyptic number.
256391 is a deficient number, since it is larger than the sum of its proper divisors (1).
256391 is an equidigital number, since it uses as much as digits as its factorization.
256391 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 1620, while the sum is 26.
The square root of 256391 is about 506.3506690032. The cubic root of 256391 is about 63.5283523957.
The spelling of 256391 in words is "two hundred fifty-six thousand, three hundred ninety-one".
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