This was hard work:-
http://www.businessinfo.co.uk/labs/hackvertor/hackvertor.php#PEBoYXNlZ2F3YV8wKCKqwMHCw8TGyMnKy8zNzs%2FQ0dLT1NXW2Nna29zd3t%2Fg4eLj5OXm5%2Bjp6uvs7e7v8PHy8%2FT19vj5%2Bvv8%2Ff4kXyIpPmFsZXJ0KDEpPEAvaGFzZWdhd2FfMD4%3D
I've reduced the code to generate the code block rather than each letter and now it's possible to define your own variables.
I could randomise the number generation and expressions too, I might do it
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"People who say it cannot be done should not interrupt those who are doing it.";
labs : [
www.businessinfo.co.uk]
blog : [
www.thespanner.co.uk]
Hackvertor : [
hackvertor.co.uk]