MathDB
IMO Shortlist 2009 - Problem C2

Source:

July 5, 2010
combinatoricsExtremal combinatoricsIMO Shortlist

Problem Statement

For any integer n2n\geq 2, let N(n)N(n) be the maxima number of triples (ai,bi,ci)(a_i, b_i, c_i), i=1,,N(n)i=1, \ldots, N(n), consisting of nonnegative integers aia_i, bib_i and cic_i such that the following two conditions are satisfied: [*] ai+bi+ci=na_i+b_i+c_i=n for all i=1,,N(n)i=1, \ldots, N(n), [*] If iji\neq j then aiaja_i\neq a_j, bibjb_i\neq b_j and cicjc_i\neq c_j Determine N(n)N(n) for all n2n\geq 2.
Proposed by Dan Schwarz, Romania