Shown with a cast-on count of 21 stitches.  

• Row 1 (RS): Knit.
• Rows 2, 4, 6, 8, 10, 14, and 18: Purl.
• Row 3: [K2, kfb, (k1, p1, k1) in next st, kfb, k2] 3 times (33 sts).
• Row 5: [K4, kfb, (k1, p1, k1) in next st, kfb, k4] 3 times (45 sts).
• Row 7: [K6, kfb, (k1, p1, k1) in next st, kfb, k6] 3 times (57 sts).
• Row 9: [K8, kfb, (k1, p1, k1) in next st, kfb, k8] 3 times (69 sts).
• Rows 12, 16, and 20: Purl.