[bryanbibat]

wbhart got the gist of it.

Here's an even longer version of the rules:

Click/tap numbers to connect them to a chain. You can only connect numbers that are at the left, right, top, bottom of the last selected number. As a faster alternative, you can also drag/swipe through the numbers.

When the sum of the chain ends in zero (ie. sum % 10 = 0) you get rewards and side effects depending on whether the chain's length is composite or prime.

- if it's composite (e.g. chain length is 4, 6, or 8 digits long), you gain 2 seconds on your time for each digit connected. However, each digit also gives you a 1 in 4 chance of replacing a digit in the grid with a "blocker", a cell that cannot be selected. - if it's prime (e.g. 2, 3, 5), you only gain 0.5 seconds for each digit, but instead of spawning blockers, each digit now has a 1 in 5 chance of removing a blocker in the grid.

Either way, the point value of the chain is ((sum / 10) ^ 3) * 5.

So connecting 1-2-3-4 gives you 5 points and 8 extra seconds but has 4 chances of spawning blockers. On the other hand, connecting 9-3-8 gives you 40 points, 1.5 extra seconds, and 3 chances to clear blockers.

Game ends when the time runs out. The goal is 1 million points, but the game will not stop you from playing when you reach that point.