module _37

let truncations i =
    let s = string i
    let len = s.Length
    seq {
        for n in 0..(len - 1) do
            yield s.Substring(0, len - n) 
            if (n > 0) then
                yield s.Substring(len - n)
    } |> Seq.distinct |> Seq.toList |> List.map (int)

let truncatablePrimes =
    let oddOr2 i = i % 2 = 1 || i = 2
        
    let pa = 
        common.primeArray 1000000
        |> Array.filter (common.numDigits >> (Array.forall oddOr2))
        
    let isPrime n = Array.exists (fun p -> p = n) pa
    pa
    |> Array.filter ((<) 10)
    |> Array.map truncations
    |> Array.filter (List.forall isPrime)
    |> Array.map (Seq.nth 0)
    |> Array.sum