Javascript script to calculate n-th element of Triangle Numbers sequence.
// ? 2017 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
<html>
<body>
Enter a number: <input type="text" id="data">
<button onclick="calculate()">Convert</button>
<p>Triangle Number is equal to</p>
<p id="newText"></p>
<script>
function calculate(){
var data = document.getElementById("data").value;
var n = parseInt(data);
document.getElementById("newText").innerHTML = triangleNumber(n);
}
function triangleNumber(n)
{
return (n * (n + 1)) / 2;
}
</script>
</body>
</html>
Javascript Triangle Number