Project Euler 29

http://projecteuler.net/index.php?section=problems&id=29

Setは次のように使います。

let s : int Set = Set.empty
let s1 = s.Add 1
let s2 = s1.Add 2
let s3 = s2.Add 1
printfn "%A" s3   // seq [1; 2]

Addすると新たにSetが作られます。使いにくいですね。
この問題の場合は、Listを作ってそれを元にSetを作ればよいでしょう。

let s = Set.ofList [1..5]
printfn "%d" s.Count

let rec calc_exp n p =
   if n % p = 0 then
      let t = calc_exp (n / p) p
      (fst t + 1, snd t)
   else
      (0, n)

let rec fac n p =
   if n = 1 then
      []
   else if p * p > n then
      [(n, 1)]
   else
      let t = calc_exp n p
      if fst t > 0 then
         (p, fst t) :: (fac (snd t) (p + 1))
      else
         fac n (p + 1)

let rec pow n e = 
   if e = 0 then 1
   else
      let m = pow n (e / 2)
      if e % 2 = 1 then m * m * n else m * m

let factorize n = fac n 2

let pow_f f e = List.map (fun x -> (fst x, (snd x) * e)) f

let N = 100
let s = Set.ofList [ for f in List.map factorize [2..N] do
                                        for b in 2..N -> pow_f f b ]
printfn "%d" s.Count