I'm very sorry about all the inconvenience, and I would like to bear the blame. Much thanks to those who help me prepare this round. It's not their fault. And much thanks to your participation.

把序列变成一棵基环树。转化为求所有基环树环的数量之和。可以egf做。设g(n)表示n个节点的基环树森林数量，显然g(n)=n^n。设G(x)是g的egf。则n个节点的一棵基环树的数量就是F=ln G。

In mathematics, the Lambert W function, also called the omega function or product logarithm, is a multivalued function, namely the branches of the converse relation of the function f(w) = wew, where w is any complex number and ew is the exponential function.…