Number 7 has often been referred to as lucky but number 9 is Magic.
Do your nine times table and the digits in the answer always add up to 9 or a multiple of 9
1 x 9 = 9
2 x 9 = 18 (1+8=9)
3 x 9 = 27 (2+7=9)
7 x 9 = 63 (6+3=9)
11 x 9 = 99 (9+9=18) 18/2 = 9
13 x 9 = 117 (1+1+17=9)
567 x 9 = 5103 (5+1+0+3=9)
13457 x 9 = 121113 (1+2+1+1+1+3=9)
456873 x 9 = 4111857 (4+1+1+1+8+5+7=27) 27/3 = 9
123456789 x 9 = 1111111101 (1+1+1+1+1+1+1+1+0+1=9)
987654321 x 9 = 8888888889 (8+8+8+8+8+8+8+8+8+9=99) 99/9 = 9
