Let be -th triangular number, i.e. . It's obvious that for any given there's exactly one such that . (The strict algebraic proof isn't difficult and will be supplied if needed.)
Ito ay malinaw na para sa anumang naibigay na may eksaktong isa tulad na . (Ang mahigpit na algebraic patunay na ito ay hindi na mahirap at ito ay ibinibigay kung kailangan.)