Sum of Digits - Click to enlarge The Sum of Digits card:
Each column contains numbers with an identical sum of digits.
For example, upon the card “27” (sum of digits = 2+7 = 9) the player may discard any card in the column under 9, (i.e. “9”, “18” … “90”).
Multiplication Table - Click to enlarge The Multiplication Table card.
Prime Numbers - Click to enlarge The Prime Numbers card.