type BitSet = object
  mem: int
proc initBitSet(): BitSet = BitSet(mem:0)
proc initBitSet[T](values: openArray[T]): BitSet =
  for i in values:
    result.add(i)
proc contains[T](t: BitSet, val: T): bool = (t.mem and (1 shl val)) != 0
proc add[T](t: var BitSet, val: T) = t.mem = t.mem or (1 shl val)

proc isPrime235*[T](n: T): bool =
  const smalls = [2, 5, 3, 13, 17, 29, 7, 11, 19, 23, 27]
  const smallsSet = initBitSet([2, 3, 5, 7, 11, 13, 17, 19, 23, 27, 29])
  if n < 31:
    return n in smallsSet
  iterator factorCandidates(max: T): T =
    for i in smalls:
      yield i
    for i in countup(30, max, 30):  # carefully
      yield i + 1; yield i + 7
      yield i + 11; yield i + 13
      yield i + 17; yield i + 19
      yield i + 23; yield i + 29
  for i in factorCandidates(intSqrt(n)):
    if n mod i == 0:
      return false
  return true