Summation for a Python function

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SUMMARY

The discussion focuses on understanding the derivation of values in the summation for Catalan numbers, specifically the recursive formula Cn+1 = Ʃ Ck Cn-k from k = 0 to n. The initial values are established as C0 = 1, C1 = 1, C2 = 2, C3 = 5, and C4 = 14, demonstrating the calculation of subsequent terms based on previous values. The confusion arises from interpreting the summation notation and the recursive nature of the formula, which is essential for correctly deriving the values.

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BK124
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Homework Statement



For formatting sake I've copied a picture of the problem and attached it here: http://i.imgur.com/kOjTy.png

Im not worried about the coding part right now I feel I can handle that, my main issue is trying to understand how the values in the summation are derived. It seems simple enough, but I can't seem to grasp how they got the 10 values in the example there. Once I understand the summation, the coding should be easy. I just need a bit of guidance in how it all's working.

Homework Equations



Cn+1 = Ʃ Ck Cn-k from k = 0 to n

The Attempt at a Solution


Obviously
C0 = 1

Beyond that, here's what my understanding of it seems to be:
For C1
k starts at 0
C1 = C0 * C1-0 + C1 * C1-1

but this is where I get confused.
 

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I suspect one defines the process recursively. How many ways can you draw a line segment between vertices? Each way divides the polygon into two smaller polygons.

You may then have to be careful iterating cases in a way that avoids double counting.
 
BK124 said:
Cn+1 = Ʃ Ck Cn-k from k = 0 to n

The Attempt at a Solution


Obviously
C0 = 1

Beyond that, here's what my understanding of it seems to be:
For C1
k starts at 0
C1 = C0 * C1-0 + C1 * C1-1

but this is where I get confused.

hmm, i think you are reading the summation notation wrong, Cn+1 doesn't come into the equation, only Cn, the previous term.
C1 = C0*C0 = 1
C2 = C0*C1 + C1*C0 = 2
C3 = C0*C2 + C1*C1 + C2*C0 = 5
C4 = C0*C3 + C1*C2 + C2*C1 + C3*C0 = 14
and so on...
 

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