diff --git a/004_prime_numbers.lua b/004_prime_numbers.lua
new file mode 100644
index 0000000..fd1daca
--- /dev/null
+++ b/004_prime_numbers.lua
@@ -0,0 +1,31 @@
+-- Solution --------------------------------------------------------------------
+
+function is_prime(x)
+   -- Your implementation here
+end
+
+-- Tests -----------------------------------------------------------------------
+
+local luaunit = require("luaunit.luauint")
+
+function test_1_is_not_prime()
+   luaunit.assertFalse(is_prime(1))
+end
+
+function test_2_is_prime()
+   luaunit.assertTrue(is_prime(2))
+end
+
+function test_15_is_not_prime()
+   luaunit.assertFalse(is_prime(15))
+end
+
+function test_441_is_not_prime()
+   luaunit.assertFalse(is_prime(441))
+end
+
+function test_563_is_prime()
+   luaunit.assertTrue(is_prime(563))
+end
+
+os.exit(luaunit.LuaUnit.run())