diff --git a/DIRECTORY.md b/DIRECTORY.md
index 13a360ab67f3..e1b857dfbdd3 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -10,6 +10,11 @@
   * [Newton Raphson](https://github.com/TheAlgorithms/Python/blob/master/arithmetic_analysis/newton_raphson.py)
   * [Secant Method](https://github.com/TheAlgorithms/Python/blob/master/arithmetic_analysis/secant_method.py)
 
+## Audio Filters
+  * [Butterworth Filter](https://github.com/TheAlgorithms/Python/blob/master/audio_filters/butterworth_filter.py)
+  * [Iir Filter](https://github.com/TheAlgorithms/Python/blob/master/audio_filters/iir_filter.py)
+  * [Show Response](https://github.com/TheAlgorithms/Python/blob/master/audio_filters/show_response.py)
+
 ## Backtracking
   * [All Combinations](https://github.com/TheAlgorithms/Python/blob/master/backtracking/all_combinations.py)
   * [All Permutations](https://github.com/TheAlgorithms/Python/blob/master/backtracking/all_permutations.py)
@@ -60,6 +65,7 @@
   * [Base64 Encoding](https://github.com/TheAlgorithms/Python/blob/master/ciphers/base64_encoding.py)
   * [Base85](https://github.com/TheAlgorithms/Python/blob/master/ciphers/base85.py)
   * [Beaufort Cipher](https://github.com/TheAlgorithms/Python/blob/master/ciphers/beaufort_cipher.py)
+  * [Bifid](https://github.com/TheAlgorithms/Python/blob/master/ciphers/bifid.py)
   * [Brute Force Caesar Cipher](https://github.com/TheAlgorithms/Python/blob/master/ciphers/brute_force_caesar_cipher.py)
   * [Caesar Cipher](https://github.com/TheAlgorithms/Python/blob/master/ciphers/caesar_cipher.py)
   * [Cryptomath Module](https://github.com/TheAlgorithms/Python/blob/master/ciphers/cryptomath_module.py)
@@ -106,8 +112,8 @@
 
 ## Conversions
   * [Binary To Decimal](https://github.com/TheAlgorithms/Python/blob/master/conversions/binary_to_decimal.py)
-  * [Binary To Octal](https://github.com/TheAlgorithms/Python/blob/master/conversions/binary_to_octal.py)
   * [Binary To Hexadecimal](https://github.com/TheAlgorithms/Python/blob/master/conversions/binary_to_hexadecimal.py)
+  * [Binary To Octal](https://github.com/TheAlgorithms/Python/blob/master/conversions/binary_to_octal.py)
   * [Decimal To Any](https://github.com/TheAlgorithms/Python/blob/master/conversions/decimal_to_any.py)
   * [Decimal To Binary](https://github.com/TheAlgorithms/Python/blob/master/conversions/decimal_to_binary.py)
   * [Decimal To Binary Recursion](https://github.com/TheAlgorithms/Python/blob/master/conversions/decimal_to_binary_recursion.py)
@@ -352,6 +358,7 @@
   * [Multi Heuristic Astar](https://github.com/TheAlgorithms/Python/blob/master/graphs/multi_heuristic_astar.py)
   * [Page Rank](https://github.com/TheAlgorithms/Python/blob/master/graphs/page_rank.py)
   * [Prim](https://github.com/TheAlgorithms/Python/blob/master/graphs/prim.py)
+  * [Random Graph Generator](https://github.com/TheAlgorithms/Python/blob/master/graphs/random_graph_generator.py)
   * [Scc Kosaraju](https://github.com/TheAlgorithms/Python/blob/master/graphs/scc_kosaraju.py)
   * [Strongly Connected Components](https://github.com/TheAlgorithms/Python/blob/master/graphs/strongly_connected_components.py)
   * [Tarjans Scc](https://github.com/TheAlgorithms/Python/blob/master/graphs/tarjans_scc.py)
@@ -937,6 +944,7 @@
   * [Capitalize](https://github.com/TheAlgorithms/Python/blob/master/strings/capitalize.py)
   * [Check Anagrams](https://github.com/TheAlgorithms/Python/blob/master/strings/check_anagrams.py)
   * [Check Pangram](https://github.com/TheAlgorithms/Python/blob/master/strings/check_pangram.py)
+  * [Credit Card Validator](https://github.com/TheAlgorithms/Python/blob/master/strings/credit_card_validator.py)
   * [Detecting English Programmatically](https://github.com/TheAlgorithms/Python/blob/master/strings/detecting_english_programmatically.py)
   * [Frequency Finder](https://github.com/TheAlgorithms/Python/blob/master/strings/frequency_finder.py)
   * [Indian Phone Validator](https://github.com/TheAlgorithms/Python/blob/master/strings/indian_phone_validator.py)
@@ -954,6 +962,7 @@
   * [Rabin Karp](https://github.com/TheAlgorithms/Python/blob/master/strings/rabin_karp.py)
   * [Remove Duplicate](https://github.com/TheAlgorithms/Python/blob/master/strings/remove_duplicate.py)
   * [Reverse Letters](https://github.com/TheAlgorithms/Python/blob/master/strings/reverse_letters.py)
+  * [Reverse Long Words](https://github.com/TheAlgorithms/Python/blob/master/strings/reverse_long_words.py)
   * [Reverse Words](https://github.com/TheAlgorithms/Python/blob/master/strings/reverse_words.py)
   * [Split](https://github.com/TheAlgorithms/Python/blob/master/strings/split.py)
   * [Upper](https://github.com/TheAlgorithms/Python/blob/master/strings/upper.py)
diff --git a/strings/credit_card_validator.py b/strings/credit_card_validator.py
index 3b5a1aae6dc9..3a08c4117a6b 100644
--- a/strings/credit_card_validator.py
+++ b/strings/credit_card_validator.py
@@ -11,13 +11,11 @@ def validate_initial_digits(credit_card_number: str) -> bool:
     >>> valid = "4111111111111111 41111111111111 34 35 37 412345 523456 634567"
     >>> all(validate_initial_digits(cc) for cc in valid.split())
     True
-    >>> invalid = "32323 36111111111111"
+    >>> invalid = "14 25 76 32323 36111111111111"
     >>> all(validate_initial_digits(cc) is False for cc in invalid.split())
     True
     """
-    if len(credit_card_number) < 2:
-        return False
-    return credit_card_number[0] in "456" or credit_card_number[1] in "457"
+    return credit_card_number.startswith(("34", "35", "37", "4", "5", "6"))
 
 
 def luhn_validation(credit_card_number: str) -> bool: