The Pell equation, by Edward Everett Whitford.

THE PELL EQUATION

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A. PALMSTROM, "Generalized Pellian equations," L'Intermediare des mathematiciens, vol. IV, p. 169, Paris,
1897.
The author says he has found properties of the equation,
Xi X2 X3 * * * Xn-1 Xn
XnA Xl X2 ' ' Xn-2 Xn-1
Xn-lA xnA xl... xn-3 Xn-2
xn-2A Xn-_A xnA... Xn-4 Xn-3
x2A x3A x4A... xnA xl
for n > 2. For n = 2, it is the Pell equation.
A. BOUTIN, "Developpement de /ix en fraction continue," Mathesis, vol. VII (2), p. 8, Paris, 1897.
This article contains 35 formulas for the development
of the square root of a number into a continued fraction.
On this subject see also E. Lucas in Journal de mathematiques speciales, p. 1, Paris, 1887, and Journal fuir die
reine und angewandte Mathematik, vol. XI, p. 332,
Berlin, 1834, where there are 42 formulas of this kind.
A. THUE, "Une solution de l'equation x2 - Dy2 = m,"
Archiv for Mathematik og Naturvidenskab, vol. XIX, p.
27, Christiania, 1897.
C. STORMER, "Quelques theoremes sur l'equations de
Pell x2 - Dy2 = 1, et leur applications," VidenskabsSelskabets Skrifter, No. 2, pp. 48, Christiania, 1897.
One theorem deals with the integral solutions for y of
the equations x2 - Dy2 = - 1, every prime divisor of
which divides D. There are several theorems upon
numbers of the form x2 + 1 with applications to the
theory of the Pell equation.
G. DE ROCQUIGNY, "Trouver deux entiers consecutis
dont Fun soit un carre et l'autre un triangulaire," Mathesis, vol. VII (2), p. 279, Paris, 1897.