Tricky to answer Cruncher as that scenario doesn't really come about. But as in the preamble if * exceeds the number to be coded then just use normal substitution. My suggestion would just be to go for it - I'm a maths dunce too (failed Maths 'O' - and English!) but got there - just don't be put off if it starts off looking gibberish when you encode, the strings of words appear amid some unwanted letters - by the time you've coded the first dozen pairs you should see something meaningful in and amongst.