# Project Euler 35

To create the rotations I make a “detour” by converting the number into a string and then performing the rotations on the string.

#light let primes_below v = Euler_utils.primes |> Seq.takeWhile (fun p -> p < v) |> Set.of_seq let rotate number = let number_str = number.ToString() let len = number_str.Length - 1 seq { for i in [ 1..len ] do yield int64 (number_str.Substring(i) + number_str.Substring(0,i)) } let has_rotated set number = let numbers = rotate number Seq.forall (fun v -> Set.contains v set) numbers let find_rotate_numbers number_set = number_set |> Set.filter (fun n -> has_rotated number_set n) let rec filter_rotations number_set = let numbers = Seq.to_list number_set match numbers with | head :: tail -> let rotated = rotate head let f_number_set = (Set.remove head number_set) - Set.of_seq rotated head :: (filter_rotations f_number_set) | [] -> [] let values = (find_rotate_numbers (primes_below 1000000L)) values |> Set.iter (fun v -> printfn "Value %A" v ) printfn "Values %A" values

As you might notice, I have included the function
`filter_rotations`

which takes only one of each “rotation
group”. However, this is not part of the problem and this therefore
not used to compute the final answer.