Selectable number grid

I would like to create a number grid, it should allow the following:

• Maximum of 6 number selected
• Can select, or deselect number
• Should show selected numbers below grid.
• After 6 numbers are selected, user submits & values are stored in database.

I've added a photo of the number grid.

enter image description here

I'm not quite sure where to start, If someone could please point me the right direction, it would be much appreciated.

Thank you.