The software is now owned by Sketchbook, Inc. , not Autodesk.
: If you previously purchased a retail copy or had it tied to an Autodesk account, you may be able to reinstall it if you have the original installation package (DMG) backed up. System Requirements for Mac (v2013) autodesk sketchbook designer 2013 mac osx free
This paper explores the historical significance and technical framework of Autodesk SketchBook Designer 2013 The software is now owned by Sketchbook, Inc