math.
start with 99, 9+9=18,99-18=81. Now notice starting at 99 and counting down on the chart that 81 is the 1st number with the star of david. 98, 98-17= 81 , 97, 97-16=81 ....down to 90-9=81, then it jumps to 72 for the 8s, etc.
once you have your list there ya go.
no matter what 2 digit you start with, the answer has the star of david.