Pattern

The number of stitches is divisible by 4.
Row 1 - knit all stitches purlwise
Row 2 - edge stitch, (from 1 stitch make 3, 3 stitches together purlwise) * repeat until the end of the row, edge stitch
Row 3 - all stitches purlwise
Row 4 - edge stitch,  (3 stitches together purlwise, from 1 stitch make 3) * repeat until the end of the row, edge stitch

Repeat rows 1 to 4.