IMO Shortlist 1998 problem A4


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2. travnja 2012.
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For any two nonnegative integers n and k satisfying n\geq k, we define the number c(n,k) as follows:

- c\left(n,0\right)=c\left(n,n\right)=1 for all n\geq 0;

- c\left(n+1,k\right)=2^{k}c\left(n,k\right)+c\left(n,k-1\right) for n\geq k\geq 1.

Prove that c\left(n,k\right)=c\left(n,n-k\right) for all n\geq k\geq 0.
Izvor: Međunarodna matematička olimpijada, shortlist 1998