diff --git a/lib/elixir/lib/application.ex b/lib/elixir/lib/application.ex
index 66af083f342..de8fe127fa6 100644
--- a/lib/elixir/lib/application.ex
+++ b/lib/elixir/lib/application.ex
@@ -696,7 +696,7 @@ defmodule Application do
       config :my_app, Databases.RepoTwo,
         # Another database configuration (for the same OTP app)
         ip: "localhost",
-        port: 20717
+        port: 20_717
 
       config :my_app, my_app_databases: [Databases.RepoOne, Databases.RepoTwo]
 
diff --git a/lib/elixir/lib/calendar/date.ex b/lib/elixir/lib/calendar/date.ex
index b4e365bea46..df7d07569b3 100644
--- a/lib/elixir/lib/calendar/date.ex
+++ b/lib/elixir/lib/calendar/date.ex
@@ -53,7 +53,7 @@ defmodule Date do
       iex> Date.diff(~D[2010-04-17], ~D[1970-01-01])
       14716
 
-      iex> Date.add(~D[1970-01-01], 14716)
+      iex> Date.add(~D[1970-01-01], 14_716)
       ~D[2010-04-17]
 
       iex> Date.shift(~D[1970-01-01], year: 40, month: 3, week: 2, day: 2)
diff --git a/lib/elixir/lib/calendar/iso.ex b/lib/elixir/lib/calendar/iso.ex
index 3cd9095b618..63304ef7ad3 100644
--- a/lib/elixir/lib/calendar/iso.ex
+++ b/lib/elixir/lib/calendar/iso.ex
@@ -182,7 +182,7 @@ defmodule Calendar.ISO do
 
   @type day_of_year :: 1..366
   @type quarter_of_year :: 1..4
-  @type year_of_era :: {1..10000, era}
+  @type year_of_era :: {1..10_000, era}
 
   @seconds_per_minute 60
   @seconds_per_hour 60 * 60
@@ -652,7 +652,7 @@ defmodule Calendar.ISO do
           day_fraction = time_to_day_fraction(hour, minute, second, {0, 0})
 
           {{year, month, day}, {hour, minute, second, _}} =
-            case add_day_fraction_to_iso_days({0, day_fraction}, -offset, 86400) do
+            case add_day_fraction_to_iso_days({0, day_fraction}, -offset, 86_400) do
               {0, day_fraction} ->
                 {{year, month, day}, time_from_day_fraction(day_fraction)}
 
@@ -784,13 +784,13 @@ defmodule Calendar.ISO do
 
   ## Examples
 
-      iex> Calendar.ISO.naive_datetime_from_iso_days({0, {0, 86400}})
+      iex> Calendar.ISO.naive_datetime_from_iso_days({0, {0, 86_400}})
       {0, 1, 1, 0, 0, 0, {0, 6}}
-      iex> Calendar.ISO.naive_datetime_from_iso_days({730_485, {0, 86400}})
+      iex> Calendar.ISO.naive_datetime_from_iso_days({730_485, {0, 86_400}})
       {2000, 1, 1, 0, 0, 0, {0, 6}}
-      iex> Calendar.ISO.naive_datetime_from_iso_days({730_485, {43200, 86400}})
+      iex> Calendar.ISO.naive_datetime_from_iso_days({730_485, {43_200, 86_400}})
       {2000, 1, 1, 12, 0, 0, {0, 6}}
-      iex> Calendar.ISO.naive_datetime_from_iso_days({-365, {0, 86400000000}})
+      iex> Calendar.ISO.naive_datetime_from_iso_days({-365, {0, 86_400_000_000}})
       {-1, 1, 1, 0, 0, 0, {0, 6}}
 
   """
@@ -1133,7 +1133,7 @@ defmodule Calendar.ISO do
 
   """
   @doc since: "1.8.0"
-  @spec year_of_era(year) :: {1..10000, era}
+  @spec year_of_era(year) :: {1..10_000, era}
   def year_of_era(year) when is_year_CE(year), do: {year, 1}
   def year_of_era(year) when is_year_BCE(year), do: {abs(year) + 1, 0}
 
@@ -1159,7 +1159,7 @@ defmodule Calendar.ISO do
   """
   @doc since: "1.13.0"
   @impl true
-  @spec year_of_era(year, month, day) :: {1..10000, era}
+  @spec year_of_era(year, month, day) :: {1..10_000, era}
   def year_of_era(year, _month, _day), do: year_of_era(year)
 
   @doc """
@@ -1704,11 +1704,11 @@ defmodule Calendar.ISO do
 
   ## Examples
 
-      iex> Calendar.ISO.iso_days_to_beginning_of_day({0, {0, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_beginning_of_day({0, {0, 86_400_000_000}})
       {0, {0, 86400000000}}
-      iex> Calendar.ISO.iso_days_to_beginning_of_day({730485, {43200000000, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_beginning_of_day({730_485, {43_200_000_000, 86_400_000_000}})
       {730485, {0, 86400000000}}
-      iex> Calendar.ISO.iso_days_to_beginning_of_day({730485, {46800000000, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_beginning_of_day({730_485, {46_800_000_000, 86_400_000_000}})
       {730485, {0, 86400000000}}
 
   """
@@ -1724,11 +1724,11 @@ defmodule Calendar.ISO do
 
   ## Examples
 
-      iex> Calendar.ISO.iso_days_to_end_of_day({0, {0, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_end_of_day({0, {0, 86_400_000_000}})
       {0, {86399999999, 86400000000}}
-      iex> Calendar.ISO.iso_days_to_end_of_day({730485, {43200000000, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_end_of_day({730_485, {43_200_000_000, 86_400_000_000}})
       {730485, {86399999999, 86400000000}}
-      iex> Calendar.ISO.iso_days_to_end_of_day({730485, {46800000000, 86400000000}})
+      iex> Calendar.ISO.iso_days_to_end_of_day({730_485, {46_800_000_000, 86_400_000_000}})
       {730485, {86399999999, 86400000000}}
 
   """
@@ -1888,7 +1888,7 @@ defmodule Calendar.ISO do
 
   def shift_time_unit({_days, _day_fraction} = iso_days, value, unit)
       when unit in [:second, :millisecond, :microsecond, :nanosecond] or is_integer(unit) do
-    ppd = System.convert_time_unit(86400, :second, unit)
+    ppd = System.convert_time_unit(86_400, :second, unit)
     add_day_fraction_to_iso_days(iso_days, value, ppd)
   end
 
@@ -1937,7 +1937,7 @@ defmodule Calendar.ISO do
        }) do
     [
       month: year * 12 + month,
-      second: week * 7 * 86400 + day * 86400 + hour * 3600 + minute * 60 + second,
+      second: week * 7 * 86_400 + day * 86_400 + hour * 3600 + minute * 60 + second,
       microsecond: microsecond
     ]
   end
diff --git a/lib/elixir/lib/file.ex b/lib/elixir/lib/file.ex
index 6b2c33225f0..0a79b9a0162 100644
--- a/lib/elixir/lib/file.ex
+++ b/lib/elixir/lib/file.ex
@@ -694,7 +694,7 @@ defmodule File do
       File.touch("/fakedir/b.txt", {{2018, 1, 30}, {13, 59, 59}})
       {:error, :enoent}
 
-      File.touch("/tmp/a.txt", 1544519753)
+      File.touch("/tmp/a.txt", 1_544_519_753)
       #=> :ok
 
   """
@@ -733,7 +733,7 @@ defmodule File do
       File.touch!("/fakedir/b.txt", {{2018, 1, 30}, {13, 59, 59}})
       ** (File.Error) could not touch "/fakedir/b.txt": no such file or directory
 
-      File.touch!("/tmp/a.txt", 1544519753)
+      File.touch!("/tmp/a.txt", 1_544_519_753)
 
   """
   @spec touch!(Path.t(), erlang_time() | posix_time()) :: :ok
diff --git a/lib/elixir/lib/kernel.ex b/lib/elixir/lib/kernel.ex
index dd3a4d8320f..564f9702607 100644
--- a/lib/elixir/lib/kernel.ex
+++ b/lib/elixir/lib/kernel.ex
@@ -6375,7 +6375,7 @@ defmodule Kernel do
 
   With a timeout:
 
-      iex> to_timeout(5400000)
+      iex> to_timeout(5_400_000)
       5400000
       iex> to_timeout(:infinity)
       :infinity
diff --git a/lib/elixir/lib/process.ex b/lib/elixir/lib/process.ex
index a8748b41668..ffb6ff2275d 100644
--- a/lib/elixir/lib/process.ex
+++ b/lib/elixir/lib/process.ex
@@ -839,7 +839,7 @@ defmodule Process do
   @spec flag(:min_bin_vheap_size, non_neg_integer) :: non_neg_integer
   @spec flag(:min_heap_size, non_neg_integer) :: non_neg_integer
   @spec flag(:priority, priority_level) :: priority_level
-  @spec flag(:save_calls, 0..10000) :: 0..10000
+  @spec flag(:save_calls, 0..10_000) :: 0..10_000
   @spec flag(:sensitive, boolean) :: boolean
   @spec flag(:trap_exit, boolean) :: boolean
   defdelegate flag(flag, value), to: :erlang, as: :process_flag
@@ -858,7 +858,7 @@ defmodule Process do
 
   Inlined by the compiler.
   """
-  @spec flag(pid, :save_calls, 0..10000) :: 0..10000
+  @spec flag(pid, :save_calls, 0..10_000) :: 0..10_000
   defdelegate flag(pid, flag, value), to: :erlang, as: :process_flag
 
   @doc """
diff --git a/lib/elixir/pages/getting-started/erlang-libraries.md b/lib/elixir/pages/getting-started/erlang-libraries.md
index e0bdbf4ad1e..08c6db79d6d 100644
--- a/lib/elixir/pages/getting-started/erlang-libraries.md
+++ b/lib/elixir/pages/getting-started/erlang-libraries.md
@@ -145,7 +145,7 @@ The [`:rand`](`:rand`) has functions for returning random values and setting the
 ```elixir
 iex> :rand.uniform()
 0.8175669086010815
-iex> _ = :rand.seed(:exs1024, {123, 123534, 345345})
+iex> _ = :rand.seed(:exs1024, {123, 123_534, 345_345})
 iex> :rand.uniform()
 0.5820506340260994
 iex> :rand.uniform(6)
diff --git a/lib/ex_unit/lib/ex_unit/formatter.ex b/lib/ex_unit/lib/ex_unit/formatter.ex
index 3a4bca6cb49..c018ef66024 100644
--- a/lib/ex_unit/lib/ex_unit/formatter.ex
+++ b/lib/ex_unit/lib/ex_unit/formatter.ex
@@ -182,16 +182,16 @@ defmodule ExUnit.Formatter do
 
   ## Examples
 
-      iex> format_times(%{run: 10000, async: nil, load: nil})
+      iex> format_times(%{run: 10_000, async: nil, load: nil})
       "Finished in 0.01 seconds (0.00s async, 0.01s sync)"
 
-      iex> format_times(%{run: 10000, async: nil, load: 20000})
+      iex> format_times(%{run: 10_000, async: nil, load: 20_000})
       "Finished in 0.03 seconds (0.02s on load, 0.00s async, 0.01s sync)"
 
-      iex> format_times(%{run: 10000, async: nil, load: 200_000})
+      iex> format_times(%{run: 10_000, async: nil, load: 200_000})
       "Finished in 0.2 seconds (0.2s on load, 0.00s async, 0.01s sync)"
 
-      iex> format_times(%{run: 100_000, async: 50000, load: 200_000})
+      iex> format_times(%{run: 100_000, async: 50_000, load: 200_000})
       "Finished in 0.3 seconds (0.2s on load, 0.05s async, 0.05s sync)"
 
   """
@@ -215,7 +215,7 @@ defmodule ExUnit.Formatter do
   end
 
   defp normalize_us(nil), do: 0
-  defp normalize_us(us), do: div(us, 10000)
+  defp normalize_us(us), do: div(us, 10_000)
 
   defp format_us(us) do
     if us < 10 do
diff --git a/lib/ex_unit/mix.exs b/lib/ex_unit/mix.exs
index 49325b2644f..ac2a611fb8d 100644
--- a/lib/ex_unit/mix.exs
+++ b/lib/ex_unit/mix.exs
@@ -36,7 +36,7 @@ defmodule ExUnit.MixProject do
         slowest: 0,
         slowest_modules: 0,
         stacktrace_depth: 20,
-        timeout: 60000,
+        timeout: 60_000,
         trace: false,
         after_suite: [],
         repeat_until_failure: 0,
diff --git a/lib/ex_unit/test/ex_unit_test.exs b/lib/ex_unit/test/ex_unit_test.exs
index 336b0bd4b85..2a9fa4bd8fd 100644
--- a/lib/ex_unit/test/ex_unit_test.exs
+++ b/lib/ex_unit/test/ex_unit_test.exs
@@ -211,7 +211,7 @@ defmodule ExUnitTest do
     output = capture_io(fn -> ExUnit.run() end)
     assert output =~ "** (ExUnit.TimeoutError) test timed out after 5ms"
   after
-    ExUnit.configure(timeout: 60000)
+    ExUnit.configure(timeout: 60_000)
   end
 
   test "reports slow tests" do
@@ -281,7 +281,7 @@ defmodule ExUnitTest do
     config = ExUnit.configuration()
     assert config[:trace]
     assert config[:max_cases] == 1
-    assert config[:timeout] == 60000
+    assert config[:timeout] == 60_000
   end
 
   test "sets trace when slowest is enabled" do
diff --git a/lib/logger/lib/logger/formatter.ex b/lib/logger/lib/logger/formatter.ex
index 2ed22d88af3..e2737d8b406 100644
--- a/lib/logger/lib/logger/formatter.ex
+++ b/lib/logger/lib/logger/formatter.ex
@@ -94,7 +94,7 @@ defmodule Logger.Formatter do
   > discarded.
   """
 
-  @type date :: {1970..10000, 1..12, 1..31}
+  @type date :: {1970..10_000, 1..12, 1..31}
   @type time_ms :: {0..23, 0..59, 0..59, 0..999}
   @type date_time_ms :: {date, time_ms}
 
diff --git a/lib/logger/test/logger/formatter_test.exs b/lib/logger/test/logger/formatter_test.exs
index 1fbc466e2cc..4db4c03f095 100644
--- a/lib/logger/test/logger/formatter_test.exs
+++ b/lib/logger/test/logger/formatter_test.exs
@@ -41,7 +41,7 @@ defmodule Logger.FormatterTest do
     assert truncate(~c"ol" ++ "á", 4) == ~c"ol" ++ "á"
 
     # :infinity
-    long_string = String.duplicate("foo", 10000)
+    long_string = String.duplicate("foo", 10_000)
     assert truncate(long_string, :infinity) == long_string
   end
 
diff --git a/lib/logger/test/logger/utils_test.exs b/lib/logger/test/logger/utils_test.exs
index 5cea0f41eba..992084faab2 100644
--- a/lib/logger/test/logger/utils_test.exs
+++ b/lib/logger/test/logger/utils_test.exs
@@ -64,7 +64,7 @@ defmodule Logger.UtilsTest do
   end
 
   test "with :infinity truncate" do
-    long_string = String.duplicate("foo", 10000)
+    long_string = String.duplicate("foo", 10_000)
     assert scan_inspect(~c"~ts", [long_string], :infinity) == {~c"~ts", [long_string]}
   end
 end
diff --git a/lib/mix/lib/mix/tasks/deps.partition.ex b/lib/mix/lib/mix/tasks/deps.partition.ex
index 73fd291a07f..f9898c9630d 100644
--- a/lib/mix/lib/mix/tasks/deps.partition.ex
+++ b/lib/mix/lib/mix/tasks/deps.partition.ex
@@ -95,8 +95,8 @@ defmodule Mix.Tasks.Deps.Partition do
 
     clients =
       Enum.map(1..count//1, fn _ ->
-        with {:ok, client} <- :gen_tcp.accept(socket, 15000),
-             {:ok, message} <- :gen_tcp.recv(client, 0, 15000) do
+        with {:ok, client} <- :gen_tcp.accept(socket, 15_000),
+             {:ok, message} <- :gen_tcp.recv(client, 0, 15_000) do
           :inet.setopts(client, active: true)
           index = message |> String.trim() |> String.to_integer()
           %{port: Map.fetch!(ports, index), index: index, socket: client}
diff --git a/lib/mix/lib/mix/tasks/profile.cprof.ex b/lib/mix/lib/mix/tasks/profile.cprof.ex
index 5eaf752d1c9..9bca753f133 100644
--- a/lib/mix/lib/mix/tasks/profile.cprof.ex
+++ b/lib/mix/lib/mix/tasks/profile.cprof.ex
@@ -92,7 +92,7 @@ defmodule Mix.Tasks.Profile.Cprof do
   Other caveats are the impossibility to call count trace BIFs, since breakpoints can
   only be set on BEAM code; functions calls performed by `:cprof` are not traced; the
   maximum size of a call counter is equal to the host machine's word size
-  (for example, 2147483647 in a 32-bit host).
+  (for example, `2_147_483_647` in a 32-bit host).
   """
 
   @typedoc """