I've created a website called Findagame and the first online puzzle that I've created for it is called DICEAGONS.
Diceagons is a math-based puzzle that works with shapes. A diceagon is a polygon with the face of a six-sided die in the middle. The value of a diceagon is the number of sides in the polygon multiplied by the number of pips showing in the die face. The object of the puzzle is to get the red totals to equal the green totals in the respective rows, columns, and diagonals.
You can see a screen capture of a 2×2 game below:
The simplest puzzle is the 2×2. However, it gets considerably more challenging when you go for a 3×3 game or larger. It has two difficulty levels - easy and hard. Easy only looks at the row and column totals while hard requires the diagonal totals to also match.
The site is http://findagame.findagroov.com. On that page, select Diceagons. Check it out
It's a nice game. Good luck with your site.
In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.