docs: def _find_next_prime(N):
      """Find next prime >= N"""
      def is_prime(n):
          if n % 2 == 0:
              return False
          i = 3
          while i * i <= n:
              if n % i:
                  i += 2
              else:
                  return False
          return True
      if N < 3:
          return 2
      if N % 2 == 0:
          N += 1
      for n in range(N, 2*N, 2):
          if is_prime(n):
              return n
      raise AssertionError("Failed to find a prime number between {0} and {1}...".format(N, 2*N))