my answer to https://codeiq.jp/ace/chikamune_minoru/q382

encode-num-seq.clj

(defn encoded-num-seq [n digits]
  (let [base (.length digits)
        enc1 (fn [n r]
               (let [q (quot n base) r2 (str (.charAt digits (rem n base)) r)]
                 (if (zero? q) r2 (recur q r2)) ))]
    (map #(enc1 % "") (iterate inc n)) ))

(defmacro nth [c i & nf]
  (if (and (list? c) (= (first c) 'encoded-num-seq))
    (let [(f a1 a2) c] `(first (~f (+ ~i ~a1) ~a2)))
    `(clojure.core/nth ~c ~i ~@nf) ))

encode-num-seq.rb

def enc1(n, digits, base)
  r = ''
  begin
    r.prepend digits[n % base]
  end while (n /= base) > 0
  r
end

def encoded_num_seq(n, digits)
  base = digits.size
  (n..Float::INFINITY).lazy.map{|x| enc1(x, digits, base) }
end