primes

I'm currently trying out some questions just to practice my programming skills. ( Not taking it in school or anything yet, self taught ) I came across this problem which required me to read in a number from a given txt file. This number would be N. Now I'm suppose to find the Nth prime number for N <= 10 000. After I find it, I'm suppose to print it out to another txt file. Now for most parts of the question I'm able to understand and devise a method to get N. The problem is that I'm using an array to save previously found prime numbers so as to use them to check against future numbers. Even

I am supposed to make a class PrimeNumberGenerator which has a method nextPrime that will print out all prime numbers up to a number the user inputs. Ex) Enter a Number: 20 2 3 5 7 11 13 17 19 Our teacher told us that we should use a nested for loop. I tried, but when I tried to make the inner (nested) loop, I got really confused. Here is my code: (I'm going to make a tester class later) public class PrimeGenerator { private int num; boolean isPrime; public PrimeGenerator(int n) { num = n; } public int nextPrime (int num) { for (int i=2; i < num; i++) // The first prime number is 2 and the

This is my code for finding primes using the Sieve of Eratosthenes. list = [i for i in range(2, int(raw_input("Compute primes up to what number? "))+1)] for i in list: for a in list: if a!=i and a%i == 0: list.remove(a) Trying to find a way to compress those nested for loops into some kind of generator or comprehension, but it doesn't seem that you can apply a function to a list using a comprehension. I tried using map and filter, but I can't seem to get it right. Thinking about something like this: print map(list.remove(a), filter(lambda a, i: (a%i ==0 and a!=i), [(a, i) for i in list for a

I'm curious if anyone has advice on how to use SIMD to find lists of prime numbers. Particularly I'm interested how to do this with SSE/AVX. The two algorithms I have been looking at are trial division and the Sieve of Eratosthenes. I have managed to find a way to use SSE with trial division. I found a faster way to to division which works well for a vector/scalar "Division by Invariant Integers Using Multiplication" http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1.2556 Each time I find a prime I form the results to do a fast division and save them. Then the next time I do the

I'm working my way through Real World Haskell (I'm in chapter 4) and to practice a bit off-book I've created the following program to calculate the nth prime. import System.Environment isPrime primes test = loop primes test where loop (p:primes) test | test `mod` p == 0 = False | p * p > test = True | otherwise = loop primes test primes = [2, 3] ++ loop [2, 3] 5 where loop primes test | isPrime primes test = test:(loop primes' test') | otherwise = test' `seq` (loop primes test') where test' = test + 2 primes' = primes ++ [test] main :: IO() main = do args <- getArgs print(last (take (read

This question already has an answer here: Program to find prime numbers 24 answers Fastest algorithm for primality test [closed] 10 answers I got this code that checks if a number is a prime: public static bool isPrime(int num) { if (num == 1) return false; if (num == 2) return true; int newnum = Math.Floor(Math.Sqrt(num)); for (int i = 2; i <= newnum; i++) if (num % i == 0) return false; return true; } Is there any better and faster way to check if a number is a prime? Yes there is. For one, you could check for 2 separately and then loop through only odd numbers. That would cut the search

How do I calculate the largest prime number smaller than value x? In actual fact, it doesn't have to be exact, just approximate and close to x. x is a 32 bit integer. The idea is that x is a configuration parameter. I'm using the largest prime number less than x (call it y) as the parameter to a class constructor. The value y must be a prime number. Some good info here on the function pi(x). Apparently, pi(x) = the number of primes less than x and you can approximate pi(x) with x/(log x - 1) while the n-th prime of that list of primes is equal to approximately n(log n) How fast you need the