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Number of n-trønder walks

Source: Baltic Way 2009

November 27, 2010
vectorcombinatorics proposedcombinatorics

Problem Statement

A nn-trønder walk is a walk starting at (0,0)(0, 0), ending at (2n,0)(2n, 0) with no self intersection and not leaving the first quadrant, where every step is one of the vectors (1,1)(1, 1), (1,−1)(1, -1) or (−1,1)(-1, 1). Find the number of nn-trønder walks.
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