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Find the sum of the functions

Source: Turkey NMO 2008 Problem 4

December 2, 2008
functionalgebra unsolvedalgebra

Problem Statement

f:N×ZZ f: \mathbb N \times \mathbb Z \rightarrow \mathbb Z satisfy the given conditions a) a) f(0,0)\equal{}1 , f(0,1)\equal{}1 , b) b) k{0,1} \forall k \notin \left\{0,1\right\} f(0,k)\equal{}0 and c) c) n1 \forall n \geq 1 and k k , f(n,k)\equal{}f(n\minus{}1,k)\plus{}f(n\minus{}1,k\minus{}2n) find the sum \displaystyle\sum_{k\equal{}0}^{\binom{2009}{2}}f(2008,k)