We have here a small collection of mathematical toys; namely three specialized iOS calculator applications .
The first named Caftorail is a factorial calculator, the second named Bifonacci is a Fibonacci number calculator and the third named Lucas is a Lucas number calculator.

Go to iTunes and download the app by clicking on one of the icons below, or click the link to see a few screen shots. The QR code under the link allows you to go to iTunes by taking a picture using a QR code reader application.