Number Drop

How Number Drop works

The board is a 7×7 grid, 49 squares in all, and it starts almost empty. You are handed one disc at a time with a number from 1 to 7 on it, and the only decision you make is which column to drop it into. It falls to the bottom of that column and stacks on whatever is already there.

Then the single rule of the game applies: a disc clears when its number equals the number of discs in its row, or the number in its column. A 3 sitting in a row that holds exactly three discs is gone. So is a 3 sitting in a column three deep. Nothing else clears a disc — there is no matching of colours, no lines to complete, and the numbers never combine.

That rule sounds slight, and it is what makes the whole game. Every disc you drop changes two counts at once — the count of its row and the count of its column — so a single drop can complete a disc on the other side of the board that you never touched. And when discs clear, the counts change again.

The rule applies to the disc you just dropped, too, which catches most people once. Drop a 1 onto a column holding 6, 4 and 4 and you get what you were aiming for — the column becomes four deep and both 4s go — but the 1 goes with them, because it landed in a row where it is the only disc, and a row of one is exactly what a 1 is waiting for. A 1 almost never survives its own landing. That is what makes it useful: it is the disc you play to set something off, not one you play to keep.

Chains are the game

Everything that matches goes at once, all in the same instant. Then the survivors fall, the counts are taken again, and anything that now matches clears too. That second round is the second link of a chain, and it can lead to a third, and a fourth.

Scoring is built to reward exactly this. A cleared disc is worth 10 points times the square of the link it went on — 10 on the first link, 40 on the second, 90 on the third, 160 on the fourth. A disc that goes on the third link is worth nine of the same disc going on the first, so a long chain is worth far more than the same number of discs cleared one drop at a time.

To take a real example from the board's own tests: a position holding eleven discs across two rows, with one 5 dropped into the third column, clears six discs over five links and pays 560 points. Clearing those same six discs one at a time would have paid 60.

The board plays a chain out one link at a time rather than jumping to the result. Each link lights the row or the column whose count explains it, the discs going flash away, and the survivors fall into the gaps — so you can see why each clear happened rather than only that the score went up. The score climbs link by link with it. A long chain takes a couple of seconds, which is the point.

Because a chain is set off by a single drop, the useful skill is not spotting a clear — it is arranging a board where one clear leaves another behind it. Discs whose numbers are close to their column's current depth are loaded and waiting; discs far from it are ballast.

Grey discs, and how the board fills up

Every so often a row of grey discs rises from the bottom and pushes everything up one row. Grey discs have no number showing and never clear on their own, but they are still discs: they count toward the row and column totals, so a rising row changes every count on the board at once and can set off clears by itself.

They are not permanent. A grey disc next to a disc that clears takes a crack, and a cracked grey disc that takes a second crack opens onto a number and joins the game properly. It takes two separate clears next to it, though — several discs clearing beside it in the same instant still count as one crack.

The game ends when the board can take no more: either a rising row has nothing left to push into, or the last empty square is filled. There is no time limit and no timer — every position is exactly as long as you want to think about it.

The two modes

• Normal — a grey row every 30 drops, at that pace for as long as you last. The rising rows are a steady tax and the game is about clearing faster than they arrive.
• Sequence — the gap shortens each level: 30 drops, then 25, 20, 15, 10, and 5 from there on. It starts the same and turns into a very different game around the fourth level, where a board you have not kept clear stops being recoverable.

Both modes are the same board and the same rules; only the pressure differs. Your game is saved as you play, so you can close the tab mid-board and pick it up later.

Where the game comes from

This mechanic is Drop7, published by Area/Code in 2009 and one of the few genuinely new puzzle designs of the early iPhone era. Game rules are not something anyone owns, and this is an independent implementation of them: none of the original's artwork, wording or presentation is reproduced here, and the scoring is our own. It runs entirely in your browser, with no accounts, no leaderboards and nothing uploaded.