Math Puzzle: Find the Secret System


The numbers in this triangle are arranged according to a certain system. What would the next row be?

The following numbers are shown in a pyramid arrangement. Row 1: 1; Row 2: 1, 2; Row 3: 1, 3, 2; Row 4: 4, 1, 3, 2; Row 5: 5, 4, 1, 3, 2; Row 6: 5, 4, 1, 6, 3, 2; Row 7: 5, 4, 1, 7, 6, 3, 2.

In each row n of the triangle, the integers from 1 to n are in alphabetical order. In the next row the number 8 would be added, and because “eight” comes before “five” in alphabetical order, it must be at the beginning of the row, giving us this sequence:

8 5 4 1 7 6 3 2

(Note that Scientific American’s editors had to adjust the order on this one from the original German.)

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This puzzle originally appeared in Spektrum der Wissenschaft and was reproduced with permission.



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