The game : 13

The game : 13 has one action and one target. You click a box on the board, and every adjacent box showing the same number merges into the one you clicked, which then shows that number plus one. Clicking a 4 with two 4s beside it, for example, leaves a single 5 where you clicked. The aim is to build a box worth 13.

The plus-one rule is what separates it from doubling games. A merge does not add values together; it bumps the clicked box up by a single step, however many neighbours joined it. So reaching 13 means climbing through the numbers one rung at a time. The developer, who also calls it 13: the game, says it is very easy at first and claims that few players ever reach 13. The frame is portrait, 600 by 800, and every move is a click.

Look over the board for a box with neighbours carrying the same number. Click it. All the matching boxes next to it merge into the box you clicked, and its number goes up by one. Keep doing this, building higher numbers out of lower ones, until you make a box showing 13, which is the goal of the game.

The result always lands on the box you click, so choose that box with care and put the new, higher number where it can meet more of its own kind next. Since each merge only adds one, a 12 needs another 12 beside it to become 13, so plan ahead for the high numbers you will need side by side.

A number merge puzzle on a board of boxes, in a portrait frame, played by clicking. Merging adds one to the clicked box rather than doubling it. The single goal is a box worth 13.

Point to Merge also works towards a final number but doubles values as blocks pair up, and 2048 Classic edition is the doubling format with a grid size you can change.