Leibniz harmonic triangle
The Leibniz harmonic triangle is a triangle of fractions that is related to the more famous Pascal triangle in a very simple way. Each row of the Leibniz harmonic triangle starts with the reciprocal of the row number (or the row number plus one depending on whether one starts counting from 1 or 0.) Every entry is the sum of the two numbers just below it. The entries can thus be computed sequentially left to right and top to bottom using subtraction instead of addition.