code: def carmichael() -> Iterator[int]:
      
      for m in composite():
          for a in range(2, m):
              if pow(a, m, m) != a:
                  break
          else:
              yield m
docs: Composite numbers n such that a^(n-1) == 1 (mod n) for every a coprime
      to n.
      https://oeis.org/A002997