First post! (oh wait, this isn't SlashDot?)
My entry for Team Clojure, 685 528 characters.
(defn ulam[n] (let [z (atom [1 0 0 {[0 0] " "}])
m [[0 1 1 0][2 -1 0 -1][2 0 -1 0][2 0 0 1][2 0 1 0]]
p (fn [x] (if (some #(zero? (rem x %)) (range 2 x)) " " "*"))]
(doseq [r (range 1 (inc n)) q (range (count m)) [a b dx dy] [(m q)]
s (range (+ (* a r) b))]
(let [i (inc (first @z)) x (+ dx (@z 1)) y (+ dy (@z 2))]
(reset! z [i x y (assoc (last @z) [x y] (p i))])))
(doseq [y (range (- n) (inc n))] (doseq [x (range (- n) (inc n))]
(print ((last @z) [x y]))) (println))))
(ulam (dec (.nextInt (java.util.Scanner. System/in))))---
Input:
5
Output:
* *
* *
* * *
* * *
* ** *
* *
* *
* *
* *
Input:
10
Output:
* * * *
* * *
* * *
* * *
* * * *
* * *
* * * * * *
* * * * *
* * *
* * ** * * *
* * *
* *
* * * * * *
* * * *
* *
* * * * *
* *
* * *
* * * *
