veganben · June 11, 2019 15:54
diff --git a/primefactors.html b/primefactors.html
 <!doctype html>
 <html>
 <head>
 <title>Prof Brian Cox's throw away line that 2021 has prime factors 43 and 47 got me thinking... </title>
 <style>
 html {
 	background-color: #deeded;
 }
 h1, h2, p, input, label {
 	color: #234567;
 	font-family: Tahoma;
 	font-weight: 100;
 	font-size: 1rem
 }
 h1 {
 	font-size: 2rem;
 }
 h2 {
 	font-size: 1.2rem;
 }
 input {
 	border-radius: 1px;
 	border: 1px;
 	margin-left: 8rem;
 	padding: 0.5rem;
 	margin-top: 2rem;
 	height: 2rem;
 	width: 18rem;
 }
 </style>
 <script>

 var getSqrt = function(top) {
 	return Math.floor(Math.sqrt(year));
 };

 var isPrime = function(n) {
 	var squirt = Math.ceil(Math.sqrt(n));
    for (var j = 2; j < squirt; j++) {
    	if (n % j === 0) {
        	return false;
    	}
    }
    return true;
 };

 var showPrimesForANumber = function() {
 	var yearEl = document.getElementById("year");
 	var year = yearEl.value;
 	var outputEl = document.getElementById("output");
 	var output = "";
 	var message = "";
 	outputEl.innerHTML = "calculating ...";
 	if(!isNaN(year) && year % 1 === 0) {
 		if(Math.sqrt(year) % 1 === 0) {
 			message = "The year " + year + " is itself a square (of " + Math.sqrt(year) + ")";
 		} else {
 			for(var i = 1; i < Math.ceil(Math.sqrt(year)); i++) {
 				if(isPrime(i)) {
 					var extra = "";
 					var checkit = year / i;
 					if(checkit % 1 === 0) {
 						if(isPrime(checkit)) {
 							if(i === 1) {
 								extra = " (" + year + " is itself prime)";
 							}
 							output += i + " & " + checkit + extra + "<br>";
 						}
 					}
 				}
 			}
 			if(output === "") {
 				message = "There are no unique prime factors for the year " + year;
 			} else {
 				message = "The prime factors for the year " + year + " are :<br>" + output;
 			}
 		} 
 	} else {
 		message = "that's not a year";
 	}
 	setTimeout(function() {outputEl.innerHTML = message}, 4);
 };
 </script>
 </head>
 <body>
 <h1>Find Prime Factors</h1>
 <h2>After Professor Brian Cox's throw-away line on The Infinite Monkey Cage podcast that the year 2021 had the prime factors <em>43</em> and <em>47</em>, it got me thinking.... </h2>
 <label for="year">Find the prime factors for a given year<br>
 <input id="year" name="year" placeholder="year" onblur="showPrimesForANumber()"></input>
 </label>

 <br>
 <p id="output">(hit tab to calculate) </p>
 </body>
 </html>
	<!doctype html>
	<html>
	<head>
	<title>Prof Brian Cox's throw away line that 2021 has prime factors 43 and 47 got me thinking... </title>
	<style>
	html {
	background-color: #deeded;
	}
	h1, h2, p, input, label {
	color: #234567;
	font-family: Tahoma;
	font-weight: 100;
	font-size: 1rem
	}
	h1 {
	font-size: 2rem;
	}
	h2 {
	font-size: 1.2rem;
	}
	input {
	border-radius: 1px;
	border: 1px;
	margin-left: 8rem;
	padding: 0.5rem;
	margin-top: 2rem;
	height: 2rem;
	width: 18rem;
	}
	</style>
	<script>

	var getSqrt = function(top) {
	return Math.floor(Math.sqrt(year));
	};

	var isPrime = function(n) {
	var squirt = Math.ceil(Math.sqrt(n));
	for (var j = 2; j < squirt; j++) {
	if (n % j === 0) {
	return false;
	}
	}
	return true;
	};

	var showPrimesForANumber = function() {
	var yearEl = document.getElementById("year");
	var year = yearEl.value;
	var outputEl = document.getElementById("output");
	var output = "";
	var message = "";
	outputEl.innerHTML = "calculating ...";
	if(!isNaN(year) && year % 1 === 0) {
	if(Math.sqrt(year) % 1 === 0) {
	message = "The year " + year + " is itself a square (of " + Math.sqrt(year) + ")";
	} else {
	for(var i = 1; i < Math.ceil(Math.sqrt(year)); i++) {
	if(isPrime(i)) {
	var extra = "";
	var checkit = year / i;
	if(checkit % 1 === 0) {
	if(isPrime(checkit)) {
	if(i === 1) {
	extra = " (" + year + " is itself prime)";
	}
	output += i + " & " + checkit + extra + "<br>";
	}
	}
	}
	}
	if(output === "") {
	message = "There are no unique prime factors for the year " + year;
	} else {
	message = "The prime factors for the year " + year + " are :<br>" + output;
	}
	}
	} else {
	message = "that's not a year";
	}
	setTimeout(function() {outputEl.innerHTML = message}, 4);
	};
	</script>
	</head>
	<body>
	<h1>Find Prime Factors</h1>
	<h2>After Professor Brian Cox's throw-away line on The Infinite Monkey Cage podcast that the year 2021 had the prime factors <em>43</em> and <em>47</em>, it got me thinking.... </h2>
	<label for="year">Find the prime factors for a given year<br>
	<input id="year" name="year" placeholder="year" onblur="showPrimesForANumber()"></input>
	</label>

	<br>
	<p id="output">(hit tab to calculate) </p>
	</body>
	</html>