And the wikipedia page
   [1]https://en.wikipedia.org/wiki/Combinatorial_number_system.

   If you want some more theoretical stuff, Knuth has a chapter about
   combinations that's easily googleable.

   Mark

   On 12 Sep 2016 03:01, "stef" <[2]s@ctrlc.hu> wrote:

     On Mon, Sep 12, 2016 at 11:09:06AM +1000, James A. Donald wrote:
     > I need to be able to do two of the following three tasks.
     >
     > Generate a permutation of eighteen ones and eighteen zeros with
     equal
     > probability for each permutation.  Or equivalently shuffle
     eighteen black
     > cards and eighteen red cards.
     >
     > Sequentially generate all possible permutations with each
     permutation
     > generated once and only once.
     >
     > Map between permutations and scalars, such that each permutation
     maps to
     > unique number, and the set of numbers that represents valid
     permutations is
     > dense.
     >
     > Could someone point me to the relevant literature, or literature
     for
     > converting between different representations of a permutation?
     >
     > Since there are only two classes of items being shuffled, this
     class of
     > permutations has a variety of special and convenient properties.
     [3]https://stackoverflow.com/questions/1506078/fast-
     permutation-number-permutation-mapping-algorithms
     --
     otr fp: [4]https://www.ctrlc.hu/~stef/otr.txt

References

   1. https://en.wikipedia.org/wiki/Combinatorial_number_system
   2. mailto:s@ctrlc.hu
   3. https://stackoverflow.com/questions/1506078/fast-permutation-number-permutation-mapping-algorithms
   4. https://www.ctrlc.hu/~stef/otr.txt