You can check the number of things registered in your application.
- Select the application on the developer portal.
- Click on the "Things" icon.
- Select "Metrics".
This will bring up the basic things metrics.
You can toggle "Cumulative" and "Discrete" views. "Cumulative" view will give you the total number. "Discrete" view will give you the number per day.
You can also change the data view range (e.g. 1 day, 1 week, 1 month).