please explain me what does i-1 in python user define function

Question

def is_correct(table,number):
    for i in range(1,11):
        if table[i-1]!=i * number:
            return i-1

Answer 1

i - 1 is the index of the table  which the user is providing we are subtracting 1 from it because in python the indexes start from 0.