Shown with a cast-on count of 1 stitch.  

• Row 1 (RS): Yo, k1, yo (3 sts).
• Rows 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20: Purl.
• Row 3: Yo, k3, yo (5 sts).
• Row 5: Yo, k5, yo (7 sts).
• Row 7: Yo, k7, yo (9 sts).
• Row 9: Yo, k1, yo, k1, k2tog, k1, ssk, k1, yo, k1, yo (11 sts).
• Row 11: Yo, k1, yo, k2, k2tog, k1, ssk, k2, yo, k1, yo (13 sts).
• Row 13: Yo, k2, yo, k1, yo, k1, k2tog, k1, ssk, k1, yo, k1, yo, k2, yo (17 sts).
• Row 15: Yo, k2, k2tog, k2, k2tog, yo, k1, yo, ssk, k2, ssk, k2, yo.
• Row 17: Yo, k3, k2tog, k2, yo, k3, yo, k2, ssk, k3, yo (19 sts).
• Row 19: Yo, k4, k2tog, k1, yo, k5, yo, k1, ssk, k4, yo (21 sts).