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+--
+--  Project Euler problem #3
+--
+--  The prime factors of 13195 are 5, 7, 13 and 29.
+--
+--  What is the largest prime factor of the number 600851475143 ?
+
+with Ada.Command_Line,
+     Ada.Containers.Vectors,
+     Ada.Numerics.Elementary_Functions,
+     Ada.Text_IO;
+
+use Ada.Containers,
+    Ada.Numerics.Elementary_Functions,
+    Ada.Text_IO;
+
+procedure Three is
+    package CL renames Ada.Command_Line;
+    --  For this problem, we need a 64-bit Natural subtype
+    subtype Long_Natural is Long_Integer range 0 .. Long_Integer'Last;
+
+    package Bucket is new Ada.Containers.Vectors (Index_Type => Natural,
+                                                    Element_Type => Long_Natural);
+
+
+    --  Return a Vector with all the factors for `Input`
+    function Factors_For (Input : in Long_Natural) return Bucket.Vector is
+        Result : Bucket.Vector;
+        -- Using the "Trial Division" method detailed in this Wikipedia entry:
+        -- https://secure.wikimedia.org/wikipedia/en/wiki/Prime_number#Trial_division
+        Ceiling : constant Long_Natural := Long_Natural (Sqrt (Float (Input)));
+    begin
+        for Index in 2 .. Ceiling loop
+            if (Input mod Index) = 0 then
+                Bucket.Append (Result, Index);
+            end if;
+        end loop;
+
+        return Result;
+    end Factors_For;
+
+begin
+    if CL.Argument_Count < 1 then
+        Put_Line (">>> Insufficient command line parameters!");
+        New_Line;
+        Put_Line ("Please execute with: " & CL.Command_Name & " <maxnumber>");
+        CL.Set_Exit_Status (CL.Failure);
+        return;
+    end if;
+
+    declare
+        Passed_Number : constant Long_Natural := Long_Natural'Value (CL.Argument (1));
+        Factors : constant Bucket.Vector := Factors_For (Passed_Number);
+    begin
+        Put_Line ("Looking for the largest prime factors for:" & Long_Natural'Image (Passed_Number));
+        New_Line;
+
+        for Index in 0 .. Bucket.Last_Index (Factors) loop
+            declare
+                Factor : constant Long_Natural := Bucket.Element (Factors, Index);
+                New_Factors : constant Bucket.Vector := Factors_For (Factor);
+            begin
+                if Bucket.Length (New_Factors) = 0 then
+                    Put_Line (Long_Natural'Image (Factor) & " looks like a prime");
+                end if;
+            end;
+        end loop;
+    end;
+end Three;