When representing numbers, the base refers to how many numbers there are before the system repeats. Our default number system is decimal because it has ten numbers (0-9) before returning back to 0 (in 10). The number system you use might change the way you think. In this game, recite the digits of π by clicking on the proper number system. Additionally, move the number of units (clockwise) specified in the center.

The abacus is the gold standard for practicing mental arithmetic. π is a traditional subject of memorization. Both are typically represented in base ten, so what if they were combined? This is a complex game. There are ten columns in the abacus (which uses the Japanese Soroban format). To recite a digit of π, move that number of columns to the left (when you get to the end, wrap around to the beginning). Then multiply that digit by the index that you're at, and add it to the number that's already there. It is rotated 90º to work on mobile devices.

The circle is a privileged format for representing different number systems, since all bases are cyclic. This advantage allows for a symmetry: number can be encoded statically (always in the same place) or by the distance they sit from a starting point. This game takes the latter approach. Select a number system and recite digits of π in it by rotating the given number of units counterclockwise.

Chess games often revolve around puzzles – finding a sequence of moves that are objectively better – but as speed chess becomes more and more prominent, quick perceptual problems might prove to be of use. This game is very direct. Pieces on the board are randomized, sometimes to positions that are legal but impractical. In each position, the black king is either being checked or mated. Select which at the bottom.

This is a website about changing how you think using numbers. Numbers are a fundamental part of what it means to be human; they're arguably the one subject with the generality to connect the sciences and everyday life. None of the games teach mathematical content, and some only with numbers implicitly. But in each you'll find a different angle for viewing numbers.

HTML isn't the steepest learning curve, but some of its mechanics are often overlooked. Many students overlook topics like custom attribute selectors. This can make the transition to CSS particularly difficult. In this game, a random DOM (Document Object Model) structure is generated on the left. It's represented in CSS format. Replicate it with HTML by typing in the lower right.

Have you ever been skeptical of the connection between numbers and the arts? Color is one of the most universal means of experiencing the link directly. This game asks you to be quantitative about your perception of color differences. In the upper left you're given a random color. Select the hex codes (which go 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f) in the lower right to replicate the color.

Numbers can be encoded in anything. Why not use them to learn something, like the piano? This is a very direct game. Recite the digits of π by playing the key it's mapped to on the right. The piano has twelve keys, but there are ten cardinal numbers, so two keys are skipped. You can also select from some alternate tunings, including some that are non-logarithmic.

Why does an abacus need to be linear? The abacus is effective for thinking about numbers; would changing its form change the way that happens? This is a complex game. Each slice of the circle is indexed, starting at 0-2π/5 (0) and moving counterclockwise (as in the unit circle). Recite the digits of π, and for each successive digit move that number of slices, and then add the product of the digit of π and the index you're on.