7.1 Four princesses each thought of a two-digit number, and Ivan thought of a four-digit number. After they wrote down their numbers in a row in some order, the result was 132040530321. Find Ivan's number.

Answer: 5303
Solution: Let's go through the options. Option 1320 is not suitable because the remaining part of the long number is divided into segments of two adjacent digits: $40,53,03,21$, and the segment 03 is impossible as it is not a two-digit number. Option 3204 is impossible due to the invalid segment 05 (or the segment 1 from a single digit). Option 2040 results in the segment 03, which is not possible. Option 0405 is not an option - it is a three-digit number. Option 4053 results in the impossible segment 03. Option 0530 is not possible. Option 5303 is the only possible one, as option 3032 leads to a segment of one digit 1.