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Pell's Equation #3 (Posted on 2024-06-13) Difficulty: 3 of 5
Find a non-trivial integer solution to this equation:
 x2 - 181y2 = 1.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Some Thoughts Possible Solution Comment 1 of 1
From my solution to http://perplexus.info/show.php?pid=4338&cid=70423:

The continued fraction expansion of sqrt(181) = [13; 2, 4, 1, 8, 6, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 6, 8, 1, 4, 2, 26]

This period is odd, so we need to determine the rational convergent to sqrt(181) up to the end of the second period:

[13; 2, 4, 1, 8, 6, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 6, 8, 1, 4, 2, 26, 2, 4, 1, 8, 6, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 6, 8, 1, 4, 2] = 2469645423824185801/183567298683461940

So the x and y values are respectively 2469645423824185801 and 183567298683461940.

Checking: 2469645423824185801^2-1=181*183567298683461940^2 / true

Edited on June 13, 2024, 10:34 am
  Posted by broll on 2024-06-13 10:33:26

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