MathDB
Rectangle Covering

Source: IMO LongList 1988, Mexico 2, Problem 50 of ILL

November 3, 2005
geometryrectanglecombinatorics unsolvedcombinatorics

Problem Statement

Prove that the numbers A,BA,B and CC are equal, where: - A=A= number of ways that we can cover a 2×n2 \times n rectangle with 2×12 \times 1 retangles. - B=B= number of sequences of ones and twos that add up to nn - C=k=0m(m+k2k)C= \sum^m_{k=0} \binom{m + k}{2 \cdot k} if n=2m,n = 2 \cdot m, and - C=k=0m(m+k+12k+1)C= \sum^m_{k=0} \binom{m + k + 1}{2 \cdot k + 1} if n=2m+1.n = 2 \cdot m + 1.