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| | Pell's equation |
 | | The first non-trivial solution of this Diophantine equation, from which all others are easily computed, can be found using, e.g., the cyclic method [1], known in India in the 12th century, or using the slightly less efficient but more regular English method [1] (17th century). |
 | | We define the size of the fundamental solution as the number of base 10 digits of the smallest y higher than one that solves Pell's equation (actually, we use the base 10 logarithm of the fundamental solution). |
 | | By Gauss' quadratic reciprocity law, the reverse is also true because the interesting values of A are of the form 4k+1 (it is interesting to note that, modulo 60, the only numbers that are simultaneously quadratic residues modulo 3, 4, and 5 are congruent, modulo 60, to either 1 or 49). |
| www.ieeta.pt /~tos/pell.html (585 words) |
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