BZOJ 2721 樱花

问题转化为求(n!)^2有多少个约数。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 1005000
#define mod 1000000007
using namespace std;
long long n,cnt[maxn],a[maxn];
void es_shaker()
{
    for (long long i=1;i<=n;i++)
    {
        if (a[i]!=1)
        {
            for (long long j=1;j*i<=n;j++)
            {
                while (!(a[j*i]%i))
                    a[j*i]/=i,cnt[i]++;
            }
        }
    }
}
int main()
{
    scanf("%lld",&n);
    for (long long i=1;i<=n;i++) a[i]=i;
    es_shaker();
    long long ans=1;
    for (long long i=1;i<=n;i++)
        ans=(ans*(2*cnt[i]+1))%mod;
    printf("%lld\n",ans);
    return 0;
}