n, the object is a
  named vector containing one more than the number of clusters in the sample,
  where the first item in the vector specifies the number of clusters in the
  population and each subsequent item specifies the number of stage two units
  for the cluster.  The name for the first item in the vector is arbitrary.
  Subsequent names in the vector identify clusters and must match the cluster
  IDs.  For a stratified design, the object is a named list of vectors, where
  names must match the strat