2+\frac{8}{3}+\frac{26}{9}+\dots +\frac{3^k-1}{3^{k-1}}+\frac{3^{k+1}-1}{3^k}=\frac{(2k-1)\cdot 3^k+1}{2\cdot3^{k-1}}+\frac{3^{k+1}-1}{3^k}