  This paper deals with Fountain codes, and especially with their encoding
matrices, which are required here to be invertible. A result is stated that an
encoding matrix induces a permutation. Also, a result is that encoding matrices
form a group with multiplication operation. An encoding is a transformation,
which reduces the entropy of an initially high-entropy input vector. A special
encoding matrix, with which the entropy reduction is more effective than with
matrices created by the Ideal Soliton distribution is formed. Experimental
results with entropy reduction are shown.
