David Angell is interested in number theory and combinatorics, particularly continued fractions, irrationality and transcendence. A selection of extension articles for secondary students can be found at his personal homepage.  David's book Irrationality and Transcendence in Number Theory has recently been published by Taylor & Francis/CRC Press.  Parabolic Problems: 60 Years of Mathematical Puzzles in Parabola will be published in mid-2024