=[(6/4a^n+1)-1/b^n-(3/3a^n+1)+5/2b^n]*ab
=[(18a^n+6-12a^n-3)/(4^an+1)*(3a^n+1)+3/2b^n]*ab
=[(6a^n+3)/(4a^n+1)*(3a^n+1)+3/2b^n]*ab