MathDB
2-digit numbers that are assigned 8

Source: XV May Olympiad (Olimpiada de Mayo) 2009 L1 P1

September 22, 2022
Digitsnumber theory

Problem Statement

Each two-digit natural number is assigned a digit as follows: Its digits are multiplied. If the result is a digit, this is the assigned digit. If the result is a two-digit number, these two figures are multiplied, and if the result is a digit, this is the assigned digit. Otherwise, the operation is repeated. For example, the digit assigned to 3232 is 66 since 3×=63 \times = 6; the digit assigned to 9393 is 44 since 9×3=279 \times 3 = 27, 2×7=142 \times 7 = 14, 1×4=41 \times 4 = 4. Find all the two-digit numbers that are assigned 88.