HDU5673 Robot 默慈金数

分析：

 

注：然后学了一发线性筛逆元的姿势

链接：http://blog.miskcoo.com/2014/09/linear-find-all-invert

#include<iostream>
#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cstdlib>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int N=1e6+5;
const LL mod=1e9+7;
LL f[N],inv[N];
int main(){
    inv[1]=1;
    for(int i=2;i<N;++i)
      inv[i]=inv[mod%i]*(mod-mod/i)%mod;
    f[0]=1;
    f[1]=1;
    for(int i=2;i<=N-5;++i)
      f[i]=((2*i+1)*f[i-1]%mod+(3*i-3)*f[i-2]%mod)%mod*inv[i+2]%mod;
    int T,n;
    scanf("%d",&T);
    while(T--){
      scanf("%d",&n);
      printf("%I64d\n",f[n]);
    }
    return 0;
}