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T(n+1)-T(n) , if T(n) is the no of dissimilar triangles with integers sides <=n

Source: 1980 Swedish Mathematical Competition p3

March 28, 2021
combinatorial geometrycombinatoricsIntegersgeometry

Problem Statement

Let T(n)T(n) be the number of dissimilar (non-degenerate) triangles with all side lengths integral and n\leq n. Find T(n+1)T(n)T(n+1)-T(n).