This was drawn on an iPad using the Procreate app. Procreate has a nice feature where it will automatically capture a timelapse video of your artwork as you are working on it. Here is the timelapse of the Android 21 image being created, from start to finish.
Most of the time, I use an iPad Pro with an Apple Pencil and the application Procreate to create digital artwork. I like this combination because it is like having a digital sketchpad that you can carry around with you fairly easily at all times. It is easy to use wherever you like, at a table, on a couch, while lying in bed, outside sitting in the shade, and so on.