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Problem of the Week 878

One for the New Year

What is the limit of the following monstrous continued fraction as N goes to infinity? Please note that this value is corrected from the original posted version. Thanks to Michael Schweitzer for pointing out the error.

                         1  + ...
                 N  + -----------
                       1999 + ...
       1999 +  ------------------
                       1999 + ...
                 1  + -----------
                         N  + ...
1 + -----------------------------
                       1999 + ...
                 1  +  ----------
                         N  + ...
        N   +  ------------------
                         N  + ...
               1999  + ----------
                         1  + ...

Source: Angel Dorito, Crux. Math Nov 1998


Because of the error, let me spare you the trouble of starting over. It turns out that the answer is the golden ratio. The presence of 1999 is irrelevant. The limit is the golden ratio no matter what real number is used in place of 1999.


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© Copyright 1999 Stan Wagon. Reproduced with permission.

9 February 1999