euler.fs

(* ---  0001 --- *)
[1..999]
|> List.where (fun f -> (f % 3 = 0) || (f % 5 = 0))
|> List.sum

(* ---  0002 --- *)
let fib =
    let rec f a b = seq {
        yield a
        yield! f b (a + b)
    }
    f 0 1

fib
|> Seq.takeWhile (fun n -> n < 4000000)
|> Seq.where (fun n -> n % 2 = 0)
|> Seq.sum

(* ---  0003 --- *)
let ub n =  int64 (sqrt(double(n)))

let factorsOf n =
    [2L..ub(n)] |> Seq.filter (fun x -> n % x = 0L)
 
let isPrime n = factorsOf(n) |> Seq.length = 0
 
let findMaxPrimeFactorOf n =
    [2L..ub(n)]
    |> Seq.filter (fun x -> n % x = 0L)
    |> Seq.filter isPrime
    |> Seq.max
 
let maxPrime = findMaxPrimeFactorOf(600851475143L)