Multiple of 2
Abbreviations: C: colour; k: knit; yfwd: yarn forward; sl: slip; ybk: yarn back; rep: repeat; p: purl; st: stitch
Terms: yarn forward: bring the yarn to the front (in the purl position); yarn back: put the yarn to the back ( in the knit position).
Row 1: C1: *k1, yfwd, sl 1 purlwise, ybk,* rep from * to * until end
Row 2: C1: p
Row 3: C2: k1, *k1, yfwd, sl 1 purlwise, ybk,*, rep from * to * until last st, k1
Row 4: C2: p