zzctommy

摘要： P2260 [清华集训2012]模积和 \[ \sum_{i=1}^{n}\sum_{j=1}^{m}(n\ mod\ i)\times(m\ mod\ j)\\ =\sum_{i=1}^{n}\sum_{j=1}^{m}(n-i\lfloor\dfrac{n}{i}\rfloor)(m-j\lfl 阅读全文