Exploring Pascal’s Triangle

Pascal’s Triangle (henceforth known as PT). You know – that thing you learned in maths. The Wikipedia entry, like most mathematical Wikipedia entries, reads (if your mathematical background is anything like mine) like “here’s a few things you might vaguely remember from school, oh and of course gleep = glorp”. Although I have to say, the PT entry is less opaque than most.

If you were lucky enough to have a “recreational maths” class then perhaps you studied PT more. I did have a recreational maths class in the 4th form (erm… 7th grade? I went to a public school with a nonstandard year numbering), but at the time I didn’t appreciate just how much higher level mathematics is intertwined (see trigonometry, complex numbers & calculus). Also, is it just me, or are curricula in general a bit light on actual number theory? I mean, we learn counting, and times tables, but after that it gets a bit fuzzy. Prime numbers? Some cursory investigation. But ISTM that students don’t really get to know the normal counting numbers very well. At least, I didn’t. I remember the occasions where we did take a lesson “off the curriculum” to study them as being some of my favourite maths lessons, e.g. the Hotel Cantor with a room for every positive integer, and the Infinity Bus Line which had a bus for every positive integer, each of which had a seat for every positive integer.

Anyway, PT. The thing I knew about but didn’t appreciate the significance of. Over the last week I’ve been tackling the Project Euler problems and there are a few concerning PT. (There are many inviting an exploration of number theory, which is also very cool). After solving 34%, I decided to skip down to problem 148, “Exploring Pascal’s Triangle”. Not many people have solved this, I thought: daunting! But also, this is my old friend PT. I’d like to get to know it better.

So after a couple of days of head scratching, I realised a way to attack the problem which would terminate before the heat death of the universe (always a useful approach to take). I also coded up some naive programs just to start exploring PT (as the problem says) – in the hope that they would give me some insight. Well, that and 3 or 4 pages of diagramming and scribbling later, I found out some quite interesting things. And I realised that I could solve the problem not just for multiples of 7, but for multiples of any prime. Now that’s cool.

I coded up a solution and ran it. It produced the wrong answer. I realised I’d missed something and corrected it. It produced the wrong answer. I tried again. Wrong answer. So I went to bed. Next morning, I realised my error, and also that I could simplify the program and speed it up. I coded it up again, and after ironing out a few non-algorithmic bugs, I ran it. Hooray! The right answer! I join the club of people who have solved problem 148.

Maths is cool.

One Response to “Exploring Pascal’s Triangle”

  1. Skye says:

    Well done you.

    The more I’m in the world, the more silly I think what we choose to teach children is. Well the basics, that’s great of course, but HOW we teach is also a bit silly. Let’s tell them “You have to just do this now, but LOOK what you can use it for in higher physics!” OK they may not understand but give them the chance to have perspective and vision, sheesh!

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