Multiple of 2 + 1
Abreviations: C: colour. k: knit; p:purl; sl 1: slip 1 yfwd: yarn forward; ybk: yarn back; rep: repeat
Row 1: C1: k
Row 2: C1: p
Row 3: C2: k1 *sl 1 purlwise, k1*, repeat from * to * until end
Row 4: C2: *k1, yfwd, sl 1 purlwise, ybk*, rep from * to * until last st, k1
These 4 rows form the pattern. Repeat as required.