diff --git a/problems/lib/euler.ex b/problems/lib/euler.ex
deleted file mode 100644
index 8626827..0000000
--- a/problems/lib/euler.ex
+++ /dev/null
@@ -1,6 +0,0 @@
-defmodule Euler do
-  def f() do
-    IO.puts("Hello, world")
-  end
-end
-
diff --git a/problems/lib/euler/algebra.ex b/problems/lib/euler/algebra.ex
new file mode 100644
index 0000000..e871898
--- /dev/null
+++ b/problems/lib/euler/algebra.ex
@@ -0,0 +1,26 @@
+defmodule Euler.Algebra do
+  def divisors(n) do
+    [ 1 |
+    (for i <- 2..floor(:math.sqrt(n))//1,
+      j = div(n, i),
+      j == n / i do
+        if i !== j, do: [i,j], else: [i]
+    end |> Enum.flat_map(&(&1))) ]
+  end
+
+  defp fact(1, acc), do: acc
+  defp fact(n, acc), do: fact(n - 1, n * acc)
+  @doc """
+  Computes n!
+  """
+  def fact(n), do: fact(n - 1, n)
+
+  defp digit_sum(0, acc), do: acc
+  defp digit_sum(n, acc), do: digit_sum(div(n, 10), rem(n, 10) + acc)
+  @doc """
+  Returns the sum of the digits of `n`.
+  """
+  def digit_sum(n), do: digit_sum(n, 0)
+end
+
+
diff --git a/problems/lib/problems.ex b/problems/lib/problems.ex
deleted file mode 100644
index 8e5fc7b..0000000
--- a/problems/lib/problems.ex
+++ /dev/null
@@ -1,18 +0,0 @@
-defmodule Problems do
-  @moduledoc """
-  Documentation for `Problems`.
-  """
-
-  @doc """
-  Hello world.
-
-  ## Examples
-
-      iex> Problems.hello()
-      :world
-
-  """
-  def hello do
-    :world
-  end
-end
diff --git a/problems/solutions/20/solution.exs b/problems/solutions/20/solution.exs
index ee20686..8cc32a9 100644
--- a/problems/solutions/20/solution.exs
+++ b/problems/solutions/20/solution.exs
@@ -1,15 +1,4 @@
-defmodule FactDigitSum do
-  defp fact(1, acc), do: acc
-  defp fact(n, acc), do: fact(n - 1, n * acc)
-  def fact(n), do: fact(n - 1, n)
-
-  defp digit_sum(0, acc), do: acc
-  defp digit_sum(n, acc), do: digit_sum(div(n, 10), rem(n, 10) + acc)
-  def digit_sum(n), do: digit_sum(n, 0)
-end
-
-
-FactDigitSum.fact(100)
-|> FactDigitSum.digit_sum()
+Euler.Algebra.fact(100)
+|> Euler.Algebra.digit_sum()
 |> IO.puts()
 
diff --git a/problems/solutions/21/solution.exs b/problems/solutions/21/solution.exs
index 4770dee..058b723 100644
--- a/problems/solutions/21/solution.exs
+++ b/problems/solutions/21/solution.exs
@@ -1,16 +1,5 @@
-defmodule AmicableNumbers do
-  def divisors(n) do
-    [ 1 |
-    (for i <- 2..floor(:math.sqrt(n))//1,
-      j = div(n, i),
-      j == n / i do
-        if i !== j, do: [i,j], else: [i]
-    end |> Enum.flat_map(&(&1))) ]
-  end
-end
-
 ns = for i <- 1..10_000, into: %{} do
-  {i, AmicableNumbers.divisors(i) |> Enum.sum()}
+  {i, Euler.Algebra.divisors(i) |> Enum.sum()}
 end
 
 for {a, b} <- ns,
diff --git a/problems/solutions/23/solution.exs b/problems/solutions/23/solution.exs
index ed2659e..6926673 100644
--- a/problems/solutions/23/solution.exs
+++ b/problems/solutions/23/solution.exs
@@ -1,21 +1,10 @@
-defmodule AmicableNumbers do
-  def divisors(n) do
-    [ 1 |
-    (for i <- 2..floor(:math.sqrt(n))//1,
-      j = div(n, i),
-      j == n / i do
-        if i !== j, do: [i,j], else: [i]
-    end |> Enum.flat_map(&(&1))) ]
-  end
-end
-
 defmodule Abundance do
   def is_abundant?(n) do
     cache = Process.get(:abundance, %{})
 
     case cache |> Map.get(n) do
       nil ->
-        sum = AmicableNumbers.divisors(n) |> Enum.sum()
+        sum = Euler.Algebra.divisors(n) |> Enum.sum()
         is? = sum > n
         Process.put(:abundance, Map.put(cache, n, is?))
         is?