Definition D33 Given a complex-valued sequence {an}\{a_n\}{an}, we use the notation ∑n=pqan\displaystyle\sum_{n=p}^qa_nn=p∑qan (p≤qp\leq qp≤q) to denote the sum ap+ap+1+⋯+aqa_p+a_{p+1}+\cdots+a_qap+ap+1+⋯+aq.