Update math/magic_number.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

math/magic_number.cpp

@@ -19,6 +19,11 @@
 #include <cassert>   /// for assert
 #include <iostream>  /// for io operations
 
+/**
+ * @namespace math
+ * @brief Mathematical algorithms
+ */
+namespace math {
 /**
  * Function to check if the given number is magic number or not.
  * @param n number to be checked.