Texas Instruments TI-83 PLUS - Manual (Page 189)

TI-83 Plus Sequence Graphing 186
PlotStart is the first term to be plotted. PlotStart=1 begins plotting on the
first term in the sequence. If you want plotting to begin with the fifth term
in a sequence, for example, set
PlotStart=5 . The first four terms are
evaluated but are not plotted on the graph.
PlotStep is the incremental n value for graphing only. PlotStep does not
affect sequence evaluation; it only designates which points are plotted
on the graph. If you specify
PlotStep=2 , the sequence is evaluated at
each consecutive integer, but it is plotted on the graph only at every
other integer.