Fuente TeX:

x= \sum_{j=1}^r k_{1j}\cdots k_{nj} p_1^{m_1} \cdots p_n^{m_n} = \left[  \sum_{j=1}^r k_{1j}\cdots k_{nj} \right] p_1^{m_1} \cdots p_n^{m_n} =a p_1^{m_1} \cdots p_n^{m_n}