Dear Group,

Many years ago I read a fascinating article which I can't seem to find
anymore.  It was about writing down (in english) the numbers from one to
a billion? and being able to retrieve the nth letter.  ie:

onetwothreefourfive...ninehundredninetymillion....ninetynineonebillion

I remember it used near semi rings and automatic differentiation, but no
matter how I use those words to search (both google and duckduck)  I
can't find it.  Do any of you have a pointer.  I believe the code was
written in haskell too.

Best wishes,
Henry Laxen