You are right. I know you are not supposed to 'invent the wheel again' but this exercise is great to learn algorithmic thinking and complex concepts like recursion.

8**7 = 2' 097' 152. And this is already more than the amount you mentioned.

The description is clear about its purpose. Your comment adds no additional information.

Sudoku players often use pencil marks to visualise all remaining candidates for each sudoku cell. In this kata we'll be focusing on drawing pencil marks for any given sudoku board. We can use this visualisation for upcoming kata's concerning sudoku strategies.

It is correct, you can check it for yourself by calculating it using calculator or by hand

4^3 =      64
6^4 =    1296
2^5 =      32
8^6 =  262144
8^7 = 2097152
      _______ +
    = 2360688