angular ui router - How to set mandatory route parameters

I want to make a route with has a mandatory parameter. If not, it should fall into

$urlRouterProvider.otherwise("/home");

Current route:

function router($stateProvider) {
        $stateProvider.state("settings", {
            url: "^/settings/{id:int}",
            views: {
                main: {
                    controller: "SettingsController",
                    templateUrl: "settings.html"
                }
            }
        });

    }

Currently both the routes below are valid:

1. http://myapp/settings //Should be invalid route


2. http://myapp/settings/123

Any ideas?