michael@0: /*
michael@0:  * Any copyright is dedicated to the Public Domain.
michael@0:  * http://creativecommons.org/licenses/publicdomain/
michael@0:  */
michael@0: 
michael@0: // Some simple testing of new, eval and some string stuff.
michael@0: 
michael@0: // constructor -- expression array initialization
michael@0: function ExprArray(n,v)
michael@0: {
michael@0:     // Initializes n values to v coerced to a string.
michael@0:     for (var i = 0; i < n; i++) {
michael@0: 	this[i] = "" + v;
michael@0:     }
michael@0: }
michael@0: 
michael@0: 
michael@0: // Print the perfect numbers up to n and the sum expression for n's divisors.
michael@0: function perfect(n)
michael@0: {
michael@0:     print("The perfect numbers up to " +  n + " are:");
michael@0:     var results = [];
michael@0: 
michael@0:     // We build sumOfDivisors[i] to hold a string expression for
michael@0:     // the sum of the divisors of i, excluding i itself.
michael@0:     var sumOfDivisors = new ExprArray(n+1,1);
michael@0:     for (var divisor = 2; divisor <= n; divisor++) {
michael@0: 	for (var j = divisor + divisor; j <= n; j += divisor) {
michael@0: 	    sumOfDivisors[j] += " + " + divisor;
michael@0: 	}
michael@0: 	// At this point everything up to 'divisor' has its sumOfDivisors
michael@0: 	// expression calculated, so we can determine whether it's perfect
michael@0: 	// already by evaluating.
michael@0: 	if (eval(sumOfDivisors[divisor]) == divisor) {
michael@0: 	    print("" + divisor + " = " + sumOfDivisors[divisor]);
michael@0: 	    results.push(divisor);
michael@0: 	}
michael@0:     }
michael@0:     print("That's all.");
michael@0:     return results;
michael@0: }
michael@0: 
michael@0: 
michael@0: print("\nA number is 'perfect' if it is equal to the sum of its")
michael@0: print("divisors (excluding itself).\n");
michael@0: 
michael@0: reportCompare(perfect(500).join(), "6,28,496");