(defn geometric
  ([] geometric 1)
  ([n] (cons n (lazy-seq (geometric (* n 1/2))))))

(geometric)

(take 10 (geometric))

IllegalArgumentException Don't know how to create ISeq from:
java.lang.Long  clojure.lang.RT.seqFrom

(1 1/2 1/4 1/8 1/16 1/32 1/64 1/128 1/256 1/512)