primes

I was going through Eric Lippert's latest Blog post for Guidelines and rules for GetHashCode when i hit this para: We could be even more clever here; just as a List resizes itself when it gets full, the bucket set could resize itself as well, to ensure that the average bucket length stays low. Also, for technical reasons it is often a good idea to make the bucket set length a prime number, rather than 100. There are plenty of improvements we could make to this hash table. But this quick sketch of a naive implementation of a hash table will do for now. I want to keep it simple. So looks like i

One thing that always strikes me as a non-cryptographer: Why is it so important to use Prime numbers? What makes them so special in cryptography? Does anyone have a simple short explanation? (I am aware that there are many primers and that Applied Cryptography is the Bible, but as said: I am not looking to implement my own cryptographic algorithm, and the stuff that I found just made my brain explode - no 10 pages of math formulas please :)) Thanks for all the answers. I've accepted the one that made the actual concept most clear to me. Most basic and general explanation: cryptography is all

The question i'm trying to answer: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? Where am I going wrong? my prime? test seems to be the issue, but it works fine on relatively small numbers. However the prime? test gives a wrong answer with larger numbers. Is there an easier way to go about this? (define b 3) (define z 0) (define divides? (lambda (a b) (= (remainder a b) 0))) (define (prime? n) (cond ((or (= n 1) (= n 0)) false) ((even? n) false) ((= n 2) true) ((= n b) true) ((divides? n b) false) (else (and (set! b (+ b 1))

I am creating a external javascript file. This is for homework. What I am supposed to do is determine if the number that the user enters in is a prime number or not, and displays a message if it is a prime number or not. I have my code written, compiles and everything. But I am cannot seem to figure out with, no matter what number i enter in, the display message always says that that number is a prime number. Can anyone help? Here is my code: var UI; var TV; var HITS; UI = window.prompt("Enter a whole number to test as a prime number: \n", "0"); TV = parseInt(UI, 10); var DD = TV; //still

After getting through some of the SO posts , i found Sieve of Eratosthenes is the best & fastest way of generating prime numbers. I want to generate the prime numbers between two numbers, say a and b . AFAIK, in Sieve's method, the space complexity is O( b ). PS: I wrote Big-O and not Theta, because i don't know whether the space requirement can be reduced. Can we reduce the space complexity in Sieve of Eratosthenes ? If you have enough space to store all the primes up to sqrt(b) then you can sieve for the primes in the range a to b using additional space O(b-a). In Python this might look like