OJ-Problems-Source/HDOJ/4196_autoAC.cpp

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#include<iostream>
#include<cstdio>
#include<cmath>
#define N 10000000
#define MOD 1000000007
#define LL long long
using namespace std;
bool flag[N+5]={0};
int prime[1000000],cnt=0;
void Prime(){
for(int i=2;i<sqrt(N+1.0);i++){
if(flag[i])
continue;
for(int j=2;j*i<=N;j++)
flag[i*j]=true;
}
for(int i=2;i<=N;i++)
if(!flag[i])
prime[cnt++]=i;
}
int getsum(int n,int p){
int sum=0;
while(n){
sum+=n/p;
n/=p;
}
return sum;
}
LL PowMod(LL a, LL b){
LL ans=1;
while(b){
if(b&1)
ans=(ans*a)%MOD;
a=(a*a)%MOD;
b>>=1;
}
return ans;
}
LL fac[N+5];
int a;
int main(){
int n;
fac[1]=1;
for(int i=2;i<=N;i++)
fac[i]=(fac[i-1]*i)%MOD;
Prime();
while(scanf("%d",&n)!=EOF&&n){
LL ret=1;
for(int i=0;i<cnt&&prime[i]<=n;i++){
a=getsum(n,prime[i]);
if(a&1)
ret=(ret*prime[i])%MOD;
}
printf("%I64d\n",(fac[n]*PowMod(ret,MOD-2))%MOD);
}
return 0;
}