Tính A = 9999999993A = 9999999993.
Ta có:
+ 93 = 72993 = 729;
+ 993 = 970299993 = 970299;
+ 9993 = 9970029999993 = 997002999;
+ 99993 = 99992 × 9999 = 99992 (1000 − 1) = 99970002999999993 = 99992 × 9999 = 99992 (1000 − 1) = 999700029999.
Phán đoán quy luật ta được:
A = 9999999993 = 999999997000000002999999999