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.
Angell DD, 2012, 'Evaluation of Certain Legendre Symbols', American Mathematical Monthly, vol. 119, pp. 690 - 693
Angell DD, 2010, 'A family of continued fractions', Journal of Number Theory, vol. 130, pp. 904 - 911, http://dx.doi.org/10.1016/j.jnt.2009.12.003
Angell DD; Hirschhorn MD, 2005, 'A remarkable continued fraction', Bulletin of the Australian Mathematical Society, vol. 72, pp. 45 - 52
Angell DD, 1989, 'The limiting behaviour of certain sequences of continued fractions', Bulletin of the Australian Mathematical Society, vol. 38, pp. 67 - 76