Giá trị của (begin{aligned} & mathrm{B}=3+3^{3}+3^{5}+3^{7}+ldots+3^{29} end{aligned}) là

 (begin{aligned} &text {Ta có } mathrm{B}=3+3^{3}+3^{5}+3^{7}+ldots+3^{29} \ &=left(3+3^{3}+3^{5}right)+left(3^{7}+3^{9}+3^{11}right)+ldots+left(3^{25}+3^{27}+3^{29}right) \ &=273+3^{6}left(3+3^{3}+3^{5}right)+ldots+3^{24}left(3+3^{3}+3^{5}right) \ &=273+3^{6} cdot 273+ldots+3^{24} cdot 273=273 cdotleft(1+3^{6}+ldots+3^{24}right) end{aligned})