every
Usage:
every [-exact|-approx] <step>
Include only every <step>'th row in the
result, starting with the first row.
The optional -approx/-exact argument
controls whether the selection needs to be exact;
in some cases an approximate calculation can take advantage
of parallelism where an exact one cannot.
The <step> argument
may be given as a plain integer (1000),
or with embedded underscores (1_000),
or in exponential format (1e3).