Saturday

March 28, 2015

March 28, 2015

Posted by **Keira** on Saturday, June 27, 2009 at 11:39am.

You are welcome

Just as an afterthought...

There is also a set of numbers called the pyramidal numbers, they are ...

1 4 10 20 ....

Can you figure out the pattern?

(Let their name be a hint.)

- For Reimy -
**Reiny**, Saturday, June 27, 2009 at 12:00pmhttp://en.wikipedia.org/wiki/Tetrahedral_number

look at the rotating triangular pyramids and count the number of balls for the different layers

top layer: 1 ball

top two layers: 4 balls

top three layers: 10 balls

etc.

you can figure out the number of balls for any number of layers n by

n(n+1)(n+2)/6

e.g. if n=3

3(4)(5)/6 = 10

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