## Favourite Mathematician

#### Problem

During the first lesson with your new and rather eccentric mathematics teacher he continues his tradition of telling the class that if anyone can guess his favourite mathematician they will be let off homework for the rest of the year. However, if you make a wrong guess you are duty bound to wash his car every week for the rest of the year. In all the years he has taught, the sparkle on his car has been the envy of every other teacher. Despite this seemingly impossible challenge, one person has managed to work it out... your older brother!

Of course he is not going to tell you the answer, but after a little "research" you find two scraps of paper hidden inside one of his books. The first piece seems to hold a clue.

The second piece is obviously the answer you are seeking.

#### Solution

The encryption process is simple. Starting inside the centre box, the plain text is written up and outward in a clockwise spiral. Then the cipher text is formed by reading down the columns.

The secret of decryption is to produce a spiral of numbers, starting at 1 and counting up to the number of letters in the cipher text. In our cipher, the number of letters is 13:

 10 11 12 13 9 2 3 8 1 4 7 6 5

This provides a map to overlay the cipher, UEDRLELAEONHR, and it is then a simple matter of writing it down the columns:

 U L E R E E O D L N R A H

Hence the name we seek is, of course, Leonhard Euler.

Why is this system unsuitable for longer messages?
E.g. HTIWMETACUOLHNAMYBISYBEOSEEAPRSYSTEM.

What could you do to develop it into a more secure system?

Problem ID: 4 (Aug 2000)     Difficulty: 2 Star

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