XXI: 21 Puzzle Game is an online mobile game, puzzle game, is free to play on Android devices, from TMSOFT.
XXI puzzles require a sum of 21 in every row and column. Move the gems around on the board until a solution is found. All gems have a unique numerical value, but watch out for the special gem that can be either a 1 or 11. Puzzles get harder as you progress your way through all 200 levels.
Download the game at:
https://play.google.com/store/apps/details?id=com.tmsoft.xxi