To complete square 20 you need to - sl1
this means slip the next stitch on the left needle onto the right needle without knitting it.
CAST ON
Aran yarn 5mm needles - 19 stitches
Double Knitting 4mm needles - 23 stitches
Row 1 - knit
Row 2 - k1,*sl1.k1* repeat *-* to end of row
Row 3 - knit
Row 4 - k2,*sl1,k1* repeat *-* to end of the row
Work rows 1 - 4 until your work measures 4" cast off