Implemented the required functions

generate_numbers.py

@@ -1,12 +1,25 @@
 def natural_numbers(n):
-    #Returns the list of natural numbers
-    #Code here
+    return list(range(1, n + 1))
 
 
 def nth_fibonacci(n):
-    #Returns n-th fibonacci number
-    #Code here
+    if n <= 0:
+        return None
+    if n == 1:
+        return 0
+    if n == 2:
+        return 1
+
+    a, b = 0, 1
+    for _ in range(3, n + 1):
+        a, b = b, a + b
+    return b
+
 
 def is_prime(n):
-    #Return true if 'n' is prime, otherwise returns false
-    #Code here
+    if n <= 1:
+        return False
+    for i in range(2, int(n ** 0.5) + 1):
+        if n % i == 0:
+            return False
+    return True