Did you ever play 2048? It was a hipe for a few weeks or months in 2014. The aim of the game is to get a tile with the number 2048. You can get this number by swiping over the screen adding up tiles with the same number.
So if there are two tiles with the number 2 directly next to eachother you can create one tile with the number 4, just by swiping over the screen. Two tiles with a 4 can make one tile with an 8, etc.
The game 2187 is more or less the same, but now you need three tiles with the same number to add up. So three tiles with a 3 give one 9. Three times a 9 give 27, etc.
Below two screenshots of the game 2187:
This is the direct link to the Google Play store:2187 on the Google Play store