!YS-v0

defn main(n=30):
  say: yellow(n)

defn yellow(n):
  a =: +[1 2 3]
  b =: (1 .. 3).zipmap([true]:cycle)
  i =: 4
  loop a a, b b, i i:
    if n > a.#:
      ? if b.$i.! &&
           (i.gcd(a.$) == 1) &&
           (i.gcd(a:butlast.$) > 1)
      : recur:
          a.conj(i), b.assoc(i true), 5
        recur: a, b, i.++
      =>: a

defn gcd(a b):
  loop a a, b b:
    if b.?:
      recur b: a % b
      else: a