regular expression for accepting alphabets & tab key spacekey

HTML

<input>

JavaScript

var regex = new RegExp(/[123ACDEGHIJLMNOPRSTZ]/);

$("input").keydown(function (e) {
		    alert("t")
    		var firstLetter = String.fromCharCode(e.which).toUpperCase();
    		if (!firstLetter.match(/[123ACDEGHIJLMNOPRSTZ]/))
        		alert("no");
        else
        		alert("yes");
}