I repeat simple sentences in my head then add the letters up as I go, and I can reach some really big numbers, plus ifi see a signpost or writing anywhere I'll do a running tally of letters. For example, 'I can do this' translates as 1,4,6,10' which then becomes 1,5,11,21, then 1,6,17,38 and so on. I've done this since I was old enough to work out the math. It occupies the mind. I also like it if it works out as a multiple of 3, though 9 is even better.
Just me then?