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**infinitebrain****Member**- Registered: 2008-07-01
- Posts: 153

Given the sequence

find k

I found the answer as 291, through a tedious guess and check method, but I'd like someone to explain in simpler terms how to find k.

*Last edited by infinitebrain (2013-03-08 12:55:30)*

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

Hi;

You can use differences to get the answer

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**Stormtangent****Member**- Registered: 2011-09-03
- Posts: 33

Hi,

If you subtract consecutive terms, you see that you get:

Subtracting again, you get

You could find the quadratic. However, another way is to realize that

, which, after solving, gives*Last edited by Stormtangent (2013-03-08 15:25:26)*

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