MathDB
trapezoids with interior angles of 90^o, 90^o, 45^o,135^o

Source: 2001 Estonia National Olympiad Final Round grade 11 p5

March 12, 2020
trapezoidcombinatorial geometrycombinatoricslattice

Problem Statement

Consider all trapezoids in a coordinate plane with interior angles of 90o,90o,45o90^o, 90^o, 45^o and 135o135^o whose bases are parallel to a coordinate axis and whose vertices have integer coordinates. Define the size of such a trapezoid as the total number of points with integer coordinates inside and on the boundary of the trapezoid. (a) How many pairwise non-congruent such trapezoids of size 20012001 are there? (b) Find all positive integers not greater than 5050 that do not appear as sizes of any such trapezoid.