Problem 60181. Integer Persistence, Product

Test cases 4,8,9 and 10 have some incorrect values.

I don't understand where the error is.

For example, for test 4, we have the sequence $u_0 = 97$, $u_1 = 9 \times 7 = 63$, $u_2 = 6 \times 3 = 18$, $u_3 = 1 \times 8 = 8$, so $n = 3$. So, the sequence for test case 4 is 97→63→18→8 and n=3 since it took 3 steps to reach a single-digit number from 97.

Similarly, for test 8 (with a randomly chosen number from the given list): $u_0$ in L and $u_1<10$ (the elements of L are chosen so that the product of the digits always gives a number < 10).

Sorry, that was my error! I had written my code to do addition rather than multiplication, and in many, but not all, cases that gave the same result for the persistence.