System: 1657A

Three beads can represent three two-digit numbers on the calculator, namely: 12, 2 1 and 30. Solving problems by classification and enumeration: three beads on a number: 30; All three beads are single digits, which does not meet the requirements. The three beads are on different numbers: the combination of sum 3 is 1 and 2, and such numbers are 12 and 2 1.

There are "tens" and "bits" on the counter. Beads on the tenth position represent 1 a tenth position, and 1 a bead on the fourth position represents 1 a bit. There are 10 beads at the tenth position and the unit position respectively. With four beads, you can dial at most four different two digits, namely 13, 22, 3 1 40.

For example, if it means 15, you can dial 1 bead in ten digits and 5 beads in one digit, which means 1 ten, five ones, that is, 15. A counter can not only represent a number within 20, but also represent a larger number, with a maximum of 1 10. There are 10 beads at the tenth position, which is 10 at the tenth position and 100 at the digit position, which is 10, which is 10,100.