The Ledermann bound is given by the solution k for (M - k)^2 >= M + k, where M is the number of indicator variables. The maximum possible number of factors is the largest integer smaller than or equal k.
an integer indicating the number of indicator variables or a matrix of data, in which case ncol(M) is used as the number of indicator variables.
The Ledermann bound, a positive real number.
Paul Gilbert and Erik Meijer
Tom Wansbeek and Erik Meijer (2000) Measurement Error and Latent Variables in Econometrics, Amsterdam: North-Holland. (note p169.)