sequence 8, 13, 19, 26

Toronto, 2019.10.16

Today The Boy brought home math homework that was in our opinion way above the grade six level - to provide a formula that can explain the sequence 8, 13, 19, 26.

18
213
319
426

There was a set of drawings with dots connected by lines that showed the pattern developing. We had to work out the value in the next series and in the tenth. Just adding the numbers in the table it wasn't too hard to come up with an answer.

But then they wanted us to come up with the formula, and it was damn tricky. With the assistance of a spreadsheet I eventually worked it out, as follows:

((n+1)*4)+((n-1)*((n-1)+1))/2

I don't know if this is really a math problem for grade six kids, or whether this was the teacher's way of checking to see which parents are paying attention. To try to learn something of the theory behind what I'd done, I looked up the number sequence on the 'tubes and got this video which just confused the hell out of me. I guess math teaching has evolved a bit since the early 80's.

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