Numbers written in base 7 with characters ranging from 'k' to 'q', where 'k' represents the digit 0, 'l' represents the digit 1, and so on

Question

We have coded some numbers written in base 7 with characters ranging from \'k\' to \'q\', where \'k\' represents the digit 0, \'l\' represents the digit 1, and so on. The fo