euler23

euler23.fsx

type DivisorType = Deficient | Perfect | Abundant

let divisors number = {1 .. number/2} |> Seq.filter(fun n -> number % n = 0)

let sumDivisors = divisors >> Seq.sum

let divisorSumType number = match (number - sumDivisors number) with
                            | 0 -> Perfect
                            | d when d > 0 -> Deficient
                            | d -> Abundant

let abundants = [1..28123] |> List.filter(fun n -> divisorSumType n = Abundant)

let abundantPairs = Set.ofSeq <| seq { for x in abundants do
                                       for y in abundants -> x + y }

let result = {1..28123} 
             |> Seq.filter(fun n -> not <| abundantPairs.Contains n)
             |> Seq.sum

printfn "%A" result