Concept
Geometric series
A sum whose terms shrink by a fixed ratio each step, finite in total exactly when that ratio is under one.
Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.
The shape of a number's divisors
Lay a number's divisors out as a lattice with one axis per prime, and two of the most useful facts in arithmetic stop being formulas and become the width and the corner of a rectangle.
The sum that fits in one square
Half, then a quarter, then an eighth, forever. Adding infinitely many things sounds like it should give infinity, and the picture that says otherwise is a square with a corner left uncut.
Named alongside it
The objects these essays reach for when they reach for this one.
ConvergenceConvergence rateCounting two waysDissectionDivisor functionDivisor sumHarmonic seriesHasse diagramLatticeLimitMethod of exhaustionMultiplicative function