Inspired by help with stitch pattern on Ravelry.
I don't think "arrowhead ribbing" is quite the right name for this: it's definitely a rib, but "arrowhead" seems to refer to a broad range, so there may be a better term.
The swatch has 1.5 stitch repeats, and 3.5 row repeats.
Shown with a cast-on count of 15 stitches.