One idea that I had was to inline the factoring logic into twice-
composite. Who cares about the factors? We just want to know if there
are two or not:

(defn twice-composite? [n]
  (loop [ps prime-seq
         tmp n
         p-count 0]
    (if (< 2 p-count)
      false
      (if (= 1 tmp)
        (= 2 p-count)
        (let [p (first ps)]
          (if (divides? tmp p)
            (recur ps (quot tmp p) (inc p-count))
            (recur (rest ps) tmp p-count))))))
)

But this lead to even slower code.

On Nov 3, 2:15 pm, Mark Engelberg <mark.engelb...@gmail.com> wrote:
> Your Clojure implementation of your particular approach is reasonable,
> but you need a cleverer approach.  I'll send you a hint offline.

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