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======Codeforces Round #641 (Div. 2)======
=====A=====
   *题意：$f(x)$代表$x$的大于$1$最小因子，对$n$进行$k$次操作，每次加上当前的$f$值，询问最后结果
   *题解：显然从第二次开始恒为2，只需要求第一次即可
=====B=====
   *题意：给定一个数列，选出一个子序列权值递增，并且下标成倍增加，输出子序列最长长度
   *题解：从$1$开始按倍数记录即可
=====C=====
   *题意：求给定数列中所有二元组的$lcm$的$gcd$
   *题解：对于$a1$，可以得知其产生的$lcm$为${lcm(a1,a2),lcm(a1,a3),,,lcm(a1,an)}$，则其产生的$gcd$就可以化简为$lcm(a1,gcd(a2,a3,,,an))$，所以维护一个后缀去求所有项产生$gcd$的$gcd$即可
=====D=====
   *题意：给定一个数列，每次选定一个区间，将区间的数变为该区间的中位数（偶数去下标较小者），询问能否都刷成$k$
   *题解：显然没$k$必然不行，有$k$的话就找是否有相邻或者间隔为$1$的两个数$\geq k$