Palindrome Numbers

Euler4.fs

// A palindromic number reads the same both ways.
//The largest palindrome made from the product of two
//2-digit numbers is 9009 = 91 × 99.

//Find the largest palindrome made from the product of
//two 3-digit numbers.
open System

let noOfDigits = 3

let lowestCandidateFactor = pown 10 (3 - 1) //100
let highestCandidateFactor = (pown 10 3) - 1 //999

let reverse (input: string) =
    new string(input.ToCharArray() |> Array.rev)

let isParabola n =
    (string n) = reverse n

let candidateFactors = {lowestCandidateFactor .. highestCandidateFactor}

Seq.map (fun x -> (Seq.map (fun y -> x * y) candidateFactors)) candidateFactors
    |> Seq.concat
    |> Seq.filter isPalindrome
    |> Seq.max