$\eqalign{
& \sum\limits_{k = 0}^{99} {\left( {1 + 3k} \right){2^k}} = \sum\limits_{k = 0}^{99} {\left( {{2^k} + 3k*{2^k}} \right)} \cr
& = \sum\limits_{k = 0}^{99} {{2^k}} + 3*\sum\limits_{k = 0}^{99} {k*{2^k}} \cr
& \sum\limits_{k = 0}^{99} {{2^k}} \;thi\;la\;cap\;so\;nhan\;co\;ban\;roi \to tu\;tinh \cr
& \sum\limits_{k = 0}^{99} {k*{2^k}} = {2^1} + 2*{2^2} + 3*{2^3} + ... + 99*{2^{99}} = {2^{99}}\left( {{1 \over {{2^{98}}}} + {2 \over {{2^{97}}}} + {3 \over {{2^{96}}}} + ... + {{99} \over {{2^0}}}} \right) \cr
& = {2^{99}}\left( {\left( {{1 \over {{2^0}}} + {1 \over {{2^1}}} + ... + {1 \over {{2^{98}}}}} \right) + \left( {{1 \over {{2^0}}} + {1 \over {{2^1}}} + ... + {1 \over {{2^{97}}}}} \right) + \left( {{1 \over {{2^0}}} + {1 \over {{2^1}}} + ... + {1 \over {{2^{96}}}}} \right) + ... + \left( {{1 \over {{2^0}}}} \right)} \right) \cr
& = {2^{99}}\left( {2\left( {1 - {1 \over {{2^{99}}}}} \right) + 2\left( {1 - {1 \over {{2^{98}}}}} \right) + ...2\left( {1 - {1 \over {{2^2}}}} \right) + 2\left( {1 - {1 \over {{2^1}}}} \right)} \right) \cr
& = {2^{100}}\left( {99 - \left( {{1 \over {{2^1}}} + {1 \over {{2^2}}} + ... + {1 \over {{2^{99}}}}} \right)} \right) \cr
& den\;day\;thi\;de\;roi \cr
& \cr} $