[racket] Challenge: <impressive function> in 140 chars or less

Neil Toronto wrote:

> What's your favorite not just computable, but tweetable function?

(define (r n)
   (for/fold ([s 1] [l '()]) ([i n])
     (values (/ 1 (- (* 2 (floor s)) s -1)) (cons s l))))

I tweeted this to make sure it fit. I had 23 characters to spare, could 
squeeze a bit of whitespace out, then use the rest to make it more 
elegant, but I have actual work to do... --PR