Shown with a cast-on count of 3 stitches.  

• Row 1 (RS): K1, kfb, k1 (4 sts).
• Rows 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, and 38: Purl.
• Row 3: K1, [kfb] twice, k1 (6 sts).
• Row 5: K3, yo, k3 (7 sts).
• Row 7: K3, yo, k1, yo, k3 (9 sts).
• Row 9: K3, yo, k3, yo, k3 (11 sts).
• Row 11: K3, yo, k5, yo, k3 (13 sts).
• Row 13: K3, yo, k7, yo, k3 (15 sts).
• Row 15: K3, yo, k9, yo, k3 (17 sts).
• Row 17: K3, yo, k5, yo, ssk, k4, yo, k3 (19 sts).
• Row 19: K3, yo, k4, ssk, yo, k1, yo, k2tog, k4, yo, k3 (21 sts).
• Row 21: K3, yo, k4, ssk, yo, k3, yo, k2tog, k4, yo, k3 (23 sts).
• Row 23: K3, yo, k4, ssk, yo, k5, yo, k2tog, k4, yo, k3 (25 sts).
• Row 25: K3, yo, k4, ssk, yo, k7, yo, k2tog, k4, yo, k3 (27 sts).
• Row 27: K3, yo, k4, ssk, yo, k9, yo, k2tog, k4, yo, k3 (29 sts).
• Row 29: K3, yo, k4, ssk, yo, k5, yo, ssk, k4, yo, k2tog, k4, yo, k3 (31 sts).
• Row 31: K7, ssk, yo, k4, ssk, yo, k1, yo, k2tog, k4, yo, k2tog, k7.
• Row 33: K6, ssk, yo, k4, ssk, yo, k3, yo, k2tog, k4, yo, k2tog, k6.
• Row 35: K5, ssk, yo, k4, ssk, yo, k5, yo, k2tog, k4, yo, k2tog, k5.
• Row 37: K4, ssk, yo, k4, ssk, yo, k7, yo, k2tog, k4, yo, k2tog, k4.
• Row 39: K3, ssk, yo, k4, ssk, yo, k9, yo, k2tog, k4, yo, k2tog, k3.
• Row 40: P13, ssp, p1, p2tog, p13 (29 sts).
• Repeat rows 29-40.