Base rnd, each side: Multiple of 2 + corner sts.
Begin 1 st to left of corner st.
Rnd 1: Ch 3 (counts as dc), dc in each st around, placing 5 dc in each corner st, join with slip st to top of ch-3.
Rnd 2: Ch 2 (does not count as a st), BPdc around ch-3 and next dc together, *ch 1, [BPdc around next 2 dc together, ch 1]** to corner st, (BPdc, ch 3, BPdc) around corner st, rep from * around, ending last rep at **, join with slip st to first BPdc.
Rnd 3: Ch 3 (counts as dc), dc in each dc and ch-1 space around, placing 5 dc in each corner space, join with slip st to top of ch-3.
Rnd 4: Ch 6 (counts as dc and ch-3), *FPdc around next st, ch 3**, BPdc around next st, ch 3; rep from * around, ending last rep at **, join with slip st to 3rd ch of ch-6. Fasten off.