- #1
dodo
- 697
- 2
Let [tex]Q(\sqrt{k})[/tex], for some positive integer k, be the extension of the field of rationals with basis [tex](1, \sqrt{k})[/tex]. For example, in [tex]Q(\sqrt{5})[/tex] the element [tex]({1 \over 2}, {1 \over 2})[/tex] is the golden ratio = [tex]{1 \over 2} + {1 \over 2}\sqrt{5}[/tex].
Given an extension [tex]Q(\sqrt{k})[/tex], let [tex]B(n)[/tex] denote the 'Binet formula',
Conj. 1: [tex]B(n)[/tex] produces only integers, iif [tex]k \equiv 1 \ ("mod" \ 4)[/tex].
Conj. 2: When [tex]k \equiv 1 \ ("mod" \ 4)[/tex], [tex]B(n)[/tex] is the closed-form formula for the recurrence sequence
Given an extension [tex]Q(\sqrt{k})[/tex], let [tex]B(n)[/tex] denote the 'Binet formula',
[tex]B(n) = {{p^n - (1-p)^n} \over \sqrt k}[/tex], n = 0, 1, 2, ...
where [tex]p = ({1 \over 2}, {1 \over 2})[/tex].Conj. 1: [tex]B(n)[/tex] produces only integers, iif [tex]k \equiv 1 \ ("mod" \ 4)[/tex].
Conj. 2: When [tex]k \equiv 1 \ ("mod" \ 4)[/tex], [tex]B(n)[/tex] is the closed-form formula for the recurrence sequence
[tex]x_n = x_{n-1} + A \; x_{n-2}[/tex], n = 2, 3, 4, ...
[tex]x_0 = 0, \ \ x_1 = 1[/tex]
with [tex]A = {{k - 1} \over 4}[/tex].