diff --git a/problems/.formatter.exs b/problems/.formatter.exs
new file mode 100644
index 0000000..d2cda26
--- /dev/null
+++ b/problems/.formatter.exs
@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]
diff --git a/problems/.gitignore b/problems/.gitignore
new file mode 100644
index 0000000..c099ca1
--- /dev/null
+++ b/problems/.gitignore
@@ -0,0 +1,26 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+problems-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/
diff --git a/problems/lib/euler.ex b/problems/lib/euler.ex
new file mode 100644
index 0000000..8626827
--- /dev/null
+++ b/problems/lib/euler.ex
@@ -0,0 +1,6 @@
+defmodule Euler do
+  def f() do
+    IO.puts("Hello, world")
+  end
+end
+
diff --git a/problems/lib/problems.ex b/problems/lib/problems.ex
new file mode 100644
index 0000000..8e5fc7b
--- /dev/null
+++ b/problems/lib/problems.ex
@@ -0,0 +1,18 @@
+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/mix.exs b/problems/mix.exs
new file mode 100644
index 0000000..7dcaf49
--- /dev/null
+++ b/problems/mix.exs
@@ -0,0 +1,28 @@
+defmodule Problems.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :problems,
+      version: "0.1.0",
+      elixir: "~> 1.16",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end
diff --git a/problems/18/solution.livemd b/problems/solutions/18/solution.livemd
similarity index 100%
rename from problems/18/solution.livemd
rename to problems/solutions/18/solution.livemd
diff --git a/problems/19/solution.livemd b/problems/solutions/19/solution.livemd
similarity index 100%
rename from problems/19/solution.livemd
rename to problems/solutions/19/solution.livemd
diff --git a/problems/20/solution.exs b/problems/solutions/20/solution.exs
similarity index 100%
rename from problems/20/solution.exs
rename to problems/solutions/20/solution.exs
diff --git a/problems/21/solution.exs b/problems/solutions/21/solution.exs
similarity index 100%
rename from problems/21/solution.exs
rename to problems/solutions/21/solution.exs
diff --git a/problems/23/solution.exs b/problems/solutions/23/solution.exs
similarity index 100%
rename from problems/23/solution.exs
rename to problems/solutions/23/solution.exs
index 0d11334..ed2659e 100644
--- a/problems/23/solution.exs
+++ b/problems/solutions/23/solution.exs
@@ -33,6 +33,6 @@ sum = for n <- 1..28123,
     s -> s + n
 end
 
+
 (((28123*28124)/2) - sum)
 |> IO.puts()
-
diff --git a/problems/67/solution.txt b/problems/solutions/67/solution.txt
similarity index 100%
rename from problems/67/solution.txt
rename to problems/solutions/67/solution.txt