Goal & Play
Remove all but one coin by formulating mathematical equations using strings of coins. The coins that make up these equations must be orthogonally adjacent to one another (no gaps), but may be read in any of the four cardinal directions: left–right, right–left, up–down or down–up. Null coins have a value of zero, and ace coins have a value of one. Once an equation has been formulated, remove any one coin from the string that made up that equation (your choice). For example, in the above diagram, starting at space d2 and reading down–up: 2 + 2 = 4. With that equation, you could choose to remove any one of the three coins at d2, d3 or d4.
Repeat until only one coin remains (in which case you win) or until there are two or more coins remaining, none of which can be removed (in which case you lose). After learning the basics and winning a few games, keep track of your best time!