/****************************************************************************** * Compilation: javac Factors.java * Execution: java Factors n * * Computes the prime factorization of n using brute force. * * % java Factors 81 * The prime factorization of 81 is: 3 3 3 3 * * % java Factors 168 * The prime factorization of 168 is: 2 2 2 3 7 * * % java Factors 4444444444 * The prime factorization of 4444444444 is: 2 2 11 41 271 9091 * * % java Factors 4444444444444463 * The prime factorization of 4444444444444463 is: 4444444444444463 * * % java Factors 10000001400000049 * The prime factorization of 10000001400000049 is: 100000007 100000007 * * % java Factors 1000000014000000049 * The prime factorization of 1000000014000000049 is: 1000000007 1000000007 * * % java Factors 9201111169755555649 * The prime factorization of 9201111169755555649 is: 3033333343 3033333343 * * Can use these for timing tests - biggest 3, 6, 9, 12, 15, and 18 digit primes * % java Factors 997 * % java Factors 999983 * % java Factors 999999937 * % java Factors 999999999989 * % java Factors 999999999999989 * % java Factors 999999999999999989 * * Remarks * ------- * - Tests factor*factor <= n instead of factor <= n for efficiency. * * - The last two examples still take a few minutes. * ******************************************************************************/ public class Factors { public static void main(String[] args) { // command-line argument long n = Long.parseLong(args[0]); System.out.print("The prime factorization of " + n + " is: "); // for each potential factor for (long factor = 2; factor*factor <= n; factor++) { // if factor is a factor of n, repeatedly divide it out while (n % factor == 0) { System.out.print(factor + " "); n = n / factor; } } // if biggest factor occurs only once, n > 1 if (n > 1) System.out.println(n); else System.out.println(); } }