seems to work

4/index.md

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+# lab 4
+
+## ex 1
+
+In this problem, we would like to implement the algorithm to calculate the digit sum of a given natural number that can be used in detecting errors in message transmission or data storage.  
+For example:
+N = 103509, the digit sum = 1 + 0 + 3 + 5 + 0 + 9 = 18.
+N = 9512, the digit sum = 9 + 5 + 1 + 2 = 17
+
+- Write a pseudo-code to solve the above problem using Iteration.
+- Write a program from the pseudo-code and solve the Problem using Iteration.
+- Calculate the complexity. Justify your answer.
+- Write a program to solve the Problem using Recursion (with Iteration if necessary).
+- Calculate the complexity. Justify your answer.
+
+## exercise 2
+
+Write a program in C/C++ to enter a natural number n and find all sphenic numbers from 1 to n using Recursion. Calculate the complexity of the proposed algorithm.
+
+Note: A sphenic number is a product of $p \times q \times r$ where p, q, and r are three distinct prime numbers.  
+Example: $30 = 2 \times 3 \times 5$; $42 = 2 \times 3 \times 7$; $66 = 2 \times 3 \times 11$