Elements of the type 3k=3 Elements of the type 3k+1=1,7,9 Elements of the type 3k+2=2,5,11 Subsets containing one element S1=1 Subsets containing two elements S2=3C1×3C1=9 Subsets containing three elements S3=3C1×3C1+1+1=11 Subsets containing four elements S4=3C3+3C3+3C2×3C2=11 Subsets containing five elements S5=3C2×3C2×1=9 Subsets containing six elements S6=1 Subsets containing seven elements S7=1 ⇒ sum =43