n(n+1)

Also not sure what this game is called, but it contains some interesting mathematical properties. Can you see the oblong numbers (2,6,12,20,30...) in this representation?

Per Mathgym:

Readers who are familiar with the theory of music will recognise the list of oblongs as the intervals in decreasing order of consonance: Octave (1:2), Perfect Fifth (2:3), Perfect Fourth (3:4), Major Third (4:5), Minor Third (5:6), etc. It is Pythagoras who is credited with discovering this mathematical relationship between music and numbers.

This discovery, that the pitch of a note is related to the length of the string which produced it, is credited as being the spark which ignited Pythagoras' imagination and philosophy. It allowed Pythagoras a glimpse of a whole new order in the Universe, one governed by intellect and logic and capable of the sublimest of pleasures. And a glimpse was all that he needed.

With this discovery, Pythagoras and the Pythagoreans set in train a way of investigation which has proved to be one of the most productive ideas in human history - that mathematics can be used to unravel the mysteries of the Universe.