This is Pell’s equation: (1) where n is a positive integer that isn’t a perfect square. Only integer solutions for x and y are sought and if n is not a perfect square then there are infinitely many integer solutions. It can be shown that the convergents of the continued fraction (CF) for the square root of n contains a solution known as the Fundamental Solution (FS). In practice this fundamental solution is the first convergent that satisfies the equation under consideration. Once this solution is known then all other solutions can be calculated from a simple recurrence relationship. Read More

## Tag: numbers

## Parsers to Fractions to Square Roots!

The earlier post Fractions to Phi to Fibonacci! showed a simple structure for Continued Fractions (CF) and used a CF representation of the Golden Ratio to derive the terms of the Fibonacci Sequence. It also alluded to a particular notation to express a CF and here we will describe that notation, create a parser for it and calculate the square roots of some integers from their specific CFs and finally derive a general CF that can be used to find the square root of any integer. CF List Notation Essentially the CF is written as a list of ints Read More

## Kaprekar’s Constant.

Just recently I came across ‘Kaprekar’s Constant‘ and maybe Mr Kaprekar had too much spare time… but still, it is quite interesting. The idea is to take a 4 digit number where the digits are not all the same then make the largest and smallest numbers possible with these digits, subtract the smaller from the larger then rinse and repeat with the result of the subtraction. e.g start with 4123 and in fact all 4 digits ‘converge’ to 6174! Now this is too good an opportunity for some Haskell… First let’s take an integer and extract its digits Read More