Yellow chamomile head showing the arrangement in 21 (blue) and 13 (aqua) spirals. Such arrangements involving consecutive Fibonacci numbers appear in a wide variety of plants. (Wikipedia)
The classic Kata that I learned many moons ago is the Fibonacci Kata. First described to me in Kent Beck's TDD book, appendix II p211.
Start with this peusudo code.
Fib(0) should return 0
Fib(1) should return 1
Fib(1) should return 2
Fib(2) should return 3
Fib(3) should return 5
Fib(5) should return 8
... continue until you have a well factored and concise Fib() function... Red-Green-Refactor. Here is a Starter Project on gitHub.
Bob Martin is famous/nortorious for Clean Coding - he's made the Bowling Kata a standard.
Looking for more KATA... try Code Cop's Katas
Peter Kofler is a developer and completionist. "I like my code being in order. Obviously I am fanatic about code quality. After years of harassing my colleagues, I was officially appointed 'Code Cop'. "