initial commit

49.fs

@@ -0,0 +1,34 @@
+module _49
+
+open common
+
+let rec insertions x = function
+    | []             -> [[x]]
+    | (y :: ys) as l -> (x::l)::(List.map (fun x -> y::x) (insertions x ys))
+
+let rec permutations = function
+    | []      -> seq [[]]
+    | x :: xs -> Seq.concat (Seq.map (insertions x) (permutations xs))
+
+let primeSequence =
+
+    let primes =
+        primeArray 10000 |> Seq.skipWhile ((>) 999) |> Array.ofSeq
+    
+    let isPrime = isPrimeFunByArray primes
+
+    primes
+    |> Seq.map (
+            numDigits >> List.ofArray >> 
+            permutations >>
+            Seq.map (Array.ofList >> digitsNum) >>
+            Seq.filter isPrime >>
+            Seq.distinct >>
+            Seq.sort >>
+            Seq.toArray
+        )
+    |> Seq.distinct
+    |> Seq.collect (List.ofSeq >> combinations 3)
+    |> Seq.filter (fun a -> a.[2] - a.[1] = a.[1] - a.[0])
+    |> Seq.map (List.rev >> List.map (numDigits >> Array.map (string) >> Array.fold (+) "") >> List.fold (+) "")
+    //|> Seq.toArray