# Wrong, But Useful, Episode 28

/podcasts/wbu28.mp3

In this month’s exciting instalment of Wrong, But Useful, @reflectivemaths and @icecolbeveridge discuss:

- The number of the podcast: 36.16 seconds, the current world record for sorting a pack of cards
- Dave is reading The Number Devil: A Mathematical Adventure – and asks what happens if you colour in the multiples of five (and Colin gets it wrong)
- Colin has been reading @standupmaths’s Things to Make and Do in the Fourth Dimension, and enjoyed the Calkin-Wilf Tree (not the Carey-Wilf Tree as he says in the audio).
- Colin points at @onthisdayinmaths’s post on the Farey sequence
- Every number can be written as the sum of two or three triangle numbers.
- Dave recommends the Taunton Museum’s Lego exhibition and collected some facts
- Dave has a plea for open-ended maths (and other) puzzles suitable for his sixth form group; Colin recommends @chrismaslanka’s Pyrgic Puzzles; Dave asks what butlers do ((they butle.))
- It’s limerick time!
- Scott Kim, of Gödel, Escher, Bach fame, has an ambigram article
- Belated gold stars to @chrishazell72 and @notonlyahatrack for the puzzle before last; no gold stars for the last one, a solution to which is here.
- Dave’s puzzle: Langford notices that the pair of yellow bricks are separated by one block, the pair of blue bricks separated by two blocks, and the pair of red bricks are separated by three blocks. How can you do the same thing with 4 or 7? Prove it’s only possible for $n=4k - \frac 12 \pm \frac 12$.