This exercise consists of two parts:

• Write a function sum_of_squares() that calculates the sum of the first n square numbers. Hint: The formula is n * (n + 1) * (2 * n + 1) / 6.
• Create a data frame squares_data with two columns: the first column x should contain the numbers 1 to 10, the second column y should contain the sum of the squared numbers up to the corresponding value in x, i.e. the result of sum_of_squares(1:10).

(from: Cotton, 2013, Learning R, O’Reilly)