proc hailstone*(n: int): auto =
  result = @[n]
  var n = n
  while n > 1:
    if (n and 1) == 1:
      n = 3 * n + 1
    else:
      n = n div 2
    result.add n

when isMainModule:
  let h = hailstone 27
  assert h.len == 112 and h[0..3] == @[27,82,41,124] and h[h.high-3..h.high] == @[8,4,2,1]
  var m, mi = 0
  for i in 1 ..< 100_000:
    let n = hailstone(i).len
    if n > m:
      m = n
      mi = i
  echo "Maximum length ", m, " was found for hailstone(", mi, ") for numbers <100,000"