Below is the syntax highlighted version of Perfect.java
from §5.4 Computability.

/****************************************************************************** * Compilation: javac Perfect.java * Execution: java Perfect * * Searches for an odd perfect number. A perfect number is an integer * that is equal to the sum of its proper divisors. For example, 28 * is perfect since 28 = 1 + 2 + 4 + 7 + 14. * * Will this program terminate, assuming overflow never occurs? * * % java Perfect 3 * The sum of the divisors of 1 is 0 * The sum of the divisors of 4 is 3 * The sum of the divisors of 7 is 1 * The sum of the divisors of 10 is 8 * The sum of the divisors of 13 is 1 * The sum of the divisors of 16 is 15 * The sum of the divisors of 19 is 1 * The sum of the divisors of 22 is 14 * The sum of the divisors of 25 is 6 * The sum of the divisors of 28 is 28 * * % java Perfect 1 * * In the 18th century Euler proved that all *even* perfect numbers * are of the form (2^k - 1) * 2^(k-1) for some k. It is unknown whether * there are infinitely many of these. It is conjectured that no odd * perfect number exists. If one exists, it must be greater than 10^300. * * http://www.wikipedia.org/wiki/Perfect_number * * ******************************************************************************/ public class Perfect { public static void main(String[] args) { int x = Integer.parseInt(args[0]); for (long n = 1; true; n = n + x) { long sum = 0; for (long i = 1; i < n; i++) if (n % i == 0) sum = sum + i; StdOut.println("The sum of the divisors of " + n + " is " + sum); if (sum == n) break; } } }

Last updated: Fri Oct 20 14:12:12 EDT 2017.