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Let $d > 0$ be a squarefree integer and $K = \mathbb Q(\sqrt d)$. Dirichlet's Unit Theorem asserts that $$\mathcal O_K^* \cong \mathbb Z \times \{\pm 1 \}.$$

A generator of the free part of $\mathcal O_K^*$ (called a fundamental unit of $\mathcal O_K$) can be found by finding the smallest solution to Pell's equations $$x^2 - d y^2 = \pm 1$$ in positive integers, at least if $d \equiv 2,3 \pmod 4$. If $d \equiv 1 \pmod 4$, then we have to look at the equations $$x^2 - dy^2 = \pm 4$$ instead.

These Pell-type equations can be solved by using continued fractions.

I am looking for a reference that provides a complete treatment of the relationship between the above Pell-type equations, fundamental units, and continued fractions. Not every fact about continued fractions needs to be proved in the reference; there are plenty of good references here.

However, the reference should contain the theory for $d \equiv 1 \pmod 4$ as well, not only the cases $d \equiv 2,3 \pmod 4$; the image in this question seems to be what I'm looking for, however, the question is pretty old and I cannot find the reference by googling.

Marktmeister
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    Try some good intro Number Theory book, like Hardy and Wright, or Niven, Zuckerman and Montgomery, or LeVeque. – Gerry Myerson Apr 21 '24 at 13:46
  • @GerryMyerson Thanks. However, I am unable to find a complete treatment of $x^2 - dy^2 = \pm 4$ in there (at least not in Hardy-Wright, Niven-Zuckerman-Montgomery, and LeVeque Vol II; I don't have access to LeVeque, Vol I right now). – Marktmeister Apr 21 '24 at 14:42
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    I like Buell, Binary Quadratic Forms. – Will Jagy Apr 21 '24 at 16:08
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    take a look at http://zakuski.math.utsa.edu/~jagy/BLOG_2014_July_15.pdf and see simple Pell method at https://math.stackexchange.com/questions/2215918/continued-fraction – Will Jagy Apr 21 '24 at 16:18
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    @J.W.Tanner there is no systematic use of continued fractions at the links you cite in order to show Pell-type equations have a nontrivial solution. – KCd Apr 22 '24 at 03:58

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