1.clj

(defn tri*
  "Generates lazy sequence of triangular numbers"
  ([] (tri* 0 1))
  ([sum n]
    (let [new-sum (+ sum n)]
      (cons new-sum (lazy-seq (tri* new-sum (inc n))))
      ))
  )
(defn tri1*
  "Generates lazy sequence of triangular numbers"
  ([] (tri1* 0 1))
  ([sum n]
    (let [new-sum (+ sum n)]
      (cons new-sum (lazy-seq (recur new-sum (inc n))))
      ))
  )