primes

I have to print the number of ways you can represent a given number as it's prime number parts. Let me clarify: Let's say I have been given this number 7. Now, first of all, I have to find all the prime numbers that are less than 7, which are 2, 3 and 5. Now, in how many ways can I summarize those numbers (I can use one number as many times I want) so that the result equals 7? For example, number 7 has five ways: 2 + 2 + 3 2 + 3 + 2 2 + 5 3 + 2 + 2 5 + 2 I'm totally lost with this task. First I figured I'd make an array of usable elements like so: { 2, 2, 2, 3, 3, 5 } (7/2 = 3, so 2 must

I am trying to determine whether the value in a text box is prime or not using jQuery. Here is what I've tried so far, but it's not working: $("#textbx").keyup(function(){ if ($("#textbx").val().length > 0) { $("#btn").removeAttr('disabled'); } }); $("#textbx").blur(function(){ if ($("#textbx").val().length ==0) { $("#btn").attr('disabled','disabled'); } }); $("#textbx").keypress(function (e) { if (e.which!=8 && (e.which < 48 || e.which > 57)) { $("#msg").html("plz press nimber only").show().fadeOut("slow"); return false; } }); $("#btn").click(function(){ var num =parseInt($("#textbx").val());

I recently read about a faster implementation of Segmented Sieve of Eratosthenes for really big numbers. Following is an implementation of the same: function sieve(low, high) { var primeArray = [], ll = Math.sqrt(low), output = []; for (var i = 0; i < high; i++) { primeArray[i] = true; } for (var i = 2; i <= ll; i++) { if (primeArray[i]) { for (var j = i * i; j < high; j += i) { primeArray[j] = false; } } } for (var i = 2; i < ll; i++) { if(primeArray[i]) { var segmentStart = Math.floor(low/i) * i; for(var j = segmentStart; j <= high; j+=i) { primeArray[j] = false; } } } for(var i = low; i <=

I wrote the following program based on the logic that a prime number is only divisible by 1 and itself. So I just go through the process of dividing it to all numbers that are greater than one and less than itself, but I seem to have a problem since I get all entered numbers as true. Here's my code... divisible(X,Y) :- Y < X, X mod Y is 0, Y1 is Y+1, divisible(X,Y1). isprime(X) :- integer(X), X > 1, \+ divisible(X,2). Thanks in advance :) I'm a beginner in Prolog but managed to fix your problem. divisible(X,Y) :- 0 is X mod Y, !. divisible(X,Y) :- X > Y+1, divisible(X, Y+1). isPrime(2) :- true

I need to get all the prime factors of large numbers that can easily get to 1k bits. The numbers are practically random so it shouldn't be hard. How do I do it efficiently? I use C++ with GMP library. EDIT: I guess you all misunderstood me. What I mean by prime a number is to get all prime factors of the number. Sorry for my english, in my language prime and factor are the same :) clarification (from OP's other post): What I need is a way to efficiently factor(find prime factors of a number) large numbers(may get to 2048 bits) using C++ and GMP(Gnu Multiple Precession lib) or less preferably