Shown with a cast-on count of 21 stitches.  

• Row 1 (RS): K21.
• Row 2: P10, M1L, p1, M1R, p10 (23 sts).
• Row 3: K11, M1R, k1, M1L, knit (25 sts).
• Row 4: P12, M1L, p1, M1R, purl (27 sts).
• Row 5: K13, M1R, k1, M1L, knit (29 sts).
• Row 6: P14, M1L, p1, M1R, purl (31 sts).
• Row 7: K15, M1R, k1, M1L, knit (33 sts).
• Row 8: P16, M1L, p1, M1R, purl (35 sts).
• Row 9: K17, M1R, k1, M1L, knit (37 sts).
• Row 10: P18, M1L, p1, M1R, purl (39 sts).
• Row 11: K19, M1R, k1, M1L, knit (41 sts).
• Row 12: Purl.
• Row 13: K20, MB, k20.