Many thanks to Maryanne Wilford for sharing this solution to curling corrugated rib with the knitlist.
Cast on a multiple of 5 + 2
1st row: K2, (P3, K2) repeat to end
2nd row: P2, (K3, P2) repeat to end
Repeat these two rows as desired
Photo © February 25th 1999 Sarah Bradberry