Shown with a cast-on count of 33 stitches.  

• Rows 1, 3, 5, 7, 9, 11, 13, 15, 17, and 19 (WS): Purl.
• Row 2: K2, *p1, yo, ssk, k9, k2tog, yo, repeat from * to last 3 sts, k3.
• Row 4: K2, *k2, yo, ssk, k7, k2tog, yo, k1, repeat from * to last 3 sts, k3.
• Row 6: K2, *k3, yo, ssk, k5, k2tog, yo, k2, repeat from * to last 3 sts, k3.
• Row 8: K2, *k2, [yo, ssk] twice, k3, [k2tog, yo] twice, k1, repeat from * to last 3 sts, k3.
• Row 10: K2, *k3, [yo, ssk] twice, k1, [k2tog, yo] twice, k2, repeat from * to last 3 sts, k3.
• Row 12: K2, *k2, [yo, ssk] twice, yo, sl2-k1-p2sso, yo, [k2tog, yo] twice, k1, repeat from * to last 3 sts, k3.
• Row 14: K2, *k1, yo, k2, [yo, ssk] twice, k1, [k2tog, yo] twice, k2, yo, repeat from * to last 3 sts, k3 (multiple of 16 sts, plus 5).
• Row 16: K2, *k1, yo, k4, yo, ssk, sl2-k1-p2sso, k2tog, yo, k4, yo, repeat from * to last 3 sts, k3.
• Row 18: K2, *k1, yo, k5, yo, ssk, k1, k2tog, yo, k5, yo, repeat from * to last 3 sts, k3 (multiple of 18 sts, plus 5).
• Row 20: K2, *k1, yo, k5, ssk, sl2-k1-p2sso, k2tog, k5, yo, repeat from * to last 3 sts, k3 (multiple of 16 sts, plus 5).
• Row 21: BO (0 sts).