释义 |
Pell EquationA special case of the quadratic Diophantine Equation having the form
 | (1) |
where is a nonsquare Natural Number. Dörrie (1965) defines the equation as
 | (2) |
and calls it the Fermat Difference Equation. The general Pell equation was solved by the Indian mathematicianBhaskara.
Pell equations, as well as the analogous equation with a minus sign on the right, can be solved by finding the ContinuedFraction for . (The trivial solution , is ignored in all subsequent discussion.)Let denote the th Convergent , then we are looking for a convergent which obeys theidentity
 | (3) |
which turns out to always be possible since the Continued Fraction of a Quadratic Surd always becomesperiodic at some term , where , i.e.,
 | (4) |
If is Odd, then is Positive and the solution in terms of smallest Integers is and , where is the th Convergent. If is Even, then is Negative, but
 | (5) |
so the solution in smallest Integers is , . Summarizing,
 | (6) |
Given one solution (which can be found as above), a whole family of solutions can be found by takingeach side to the th Power,
 | (7) |
Factoring gives
 | (8) |
and
which gives the family of solutions
These solutions also hold for
 | (13) |
except that can take on only Odd values.
The following table gives the smallest integer solutions to the Pell equation with constant (Beiler 1966, p. 254). Square are not included, since they would result in an equation of the form
 | (14) |
which has no solutions (since the difference of two Squares cannot be 1). |  |  |  |  |  | 2 | 3 | 2 | 54 | 485 | 66 | 3 | 2 | 1 | 55 | 89 | 12 | 5 | 9 | 4 | 56 | 15 | 2 | 6 | 5 | 2 | 57 | 151 | 20 | 7 | 8 | 3 | 58 | 19603 | 2574 | 8 | 3 | 1 | 59 | 530 | 69 | 10 | 19 | 6 | 60 | 31 | 4 | 11 | 10 | 3 | 61 | 1766319049 | 226153980 | 12 | 7 | 2 | 62 | 63 | 8 | 13 | 649 | 180 | 63 | 8 | 1 | 14 | 15 | 4 | 65 | 129 | 16 | 15 | 4 | 1 | 66 | 65 | 8 | 17 | 33 | 8 | 67 | 48842 | 5967 | 18 | 17 | 4 | 68 | 33 | 4 | 19 | 170 | 39 | 69 | 7775 | 936 | 20 | 9 | 2 | 70 | 251 | 30 | 21 | 55 | 12 | 71 | 3480 | 413 | 22 | 197 | 42 | 72 | 17 | 2 | 23 | 24 | 5 | 73 | 2281249 | 267000 | 24 | 5 | 1 | 74 | 3699 | 430 | 26 | 51 | 10 | 75 | 26 | 3 | 27 | 26 | 5 | 76 | 57799 | 6630 | 28 | 127 | 24 | 77 | 351 | 40 | 29 | 9801 | 1820 | 78 | 53 | 6 | 30 | 11 | 2 | 79 | 80 | 9 | 31 | 1520 | 273 | 80 | 9 | 1 | 32 | 17 | 3 | 82 | 163 | 18 | 33 | 23 | 4 | 83 | 82 | 9 | 34 | 35 | 6 | 84 | 55 | 6 | 35 | 6 | 1 | 85 | 285769 | 30996 | 37 | 73 | 12 | 86 | 10405 | 1122 | 38 | 37 | 6 | 87 | 28 | 3 | 39 | 25 | 4 | 88 | 197 | 21 | 40 | 19 | 3 | 89 | 500001 | 53000 | 41 | 2049 | 320 | 90 | 19 | 2 | 42 | 13 | 2 | 91 | 1574 | 165 | 43 | 3482 | 531 | 92 | 1151 | 120 | 44 | 199 | 30 | 93 | 12151 | 1260 | 45 | 161 | 24 | 94 | 2143295 | 221064 | 46 | 24335 | 3588 | 95 | 39 | 4 | 47 | 48 | 7 | 96 | 49 | 5 | 48 | 7 | 1 | 97 | 62809633 | 6377352 | 50 | 99 | 14 | 98 | 99 | 10 | 51 | 50 | 7 | 99 | 10 | 1 | 52 | 649 | 90 | 101 | 201 | 20 | 53 | 66249 | 9100 | 102 | 101 | 10 |
The first few minimal values of and for nonsquare are 3, 2, 9, 5, 8, 3, 19, 10, 7, 649, ... (Sloane's A033313)and 2, 1, 4, 2, 3, 1, 6, 3, 2, 180, ... (Sloane's A033317), respectively. The values of having , 3, ... are3, 2, 15, 6, 35, 12, 7, 5, 11, 30, ... (Sloane's A033314) and the values of having , 2, ... are 3, 2, 7, 5,23, 10, 47, 17, 79, 26, ... (Sloane's A033318). Values of the incrementally largest minimal are 3, 9, 19, 649, 9801,24335, 66249, ... (Sloane's A033315) which occur at , 5, 10, 13, 29, 46, 53, 61, 109, 181, ... (Sloane's A033316). Values of the incrementally largest minimal are 2, 4, 6, 180, 1820, 3588, 9100, 226153980, ... (Sloane's A033319),which occur at , 5, 10, 13, 29, 46, 53, 61, ... (Sloane's A033320). See also Diophantine Equation, Diophantine Equation--Quadratic, Lagrange Number (Diophantine Equation) References
Beiler, A. H. ``The Pellian.'' Ch. 22 in Recreations in the Theory of Numbers: The Queen of Mathematics Entertains. New York: Dover, pp. 248-268, 1966.Degan, C. F. Canon Pellianus. Copenhagen, Denmark, 1817. Dörrie, H. 100 Great Problems of Elementary Mathematics: Their History and Solutions. New York: Dover, 1965. Lagarias, J. C. ``On the Computational Complexity of Determining the Solvability or Unsolvability of the Equation .'' Trans. Amer. Math. Soc. 260, 485-508, 1980. Sloane, N. J. A. Sequences A033313,A033314,A033315,A033316,A033317,A033318,A033319, andA033320in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html. Smarandache, F. ``Un metodo de resolucion de la ecuacion diofantica.'' Gaz. Math. 1, 151-157, 1988. Smarandache, F. `` Method to Solve the Diophantine Equation .'' In Collected Papers, Vol. 1. Lupton, AZ: Erhus University Press, 1996. Stillwell, J. C. Mathematics and Its History. New York: Springer-Verlag, 1989. Whitford, E. E. Pell Equation. New York: Columbia University Press, 1912.
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