bk = sum of ai if i | k

维护一个质因子分解之后,关于指数的前缀和。
理论时间复杂度O(nloglogn)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<vector>
#define ll long long
#define llu unsigned ll
using namespace std;

#define uint unsigned int
uint seed;
inline uint getnext(){
	seed^=seed<<13;
	seed^=seed>>17;
	seed^=seed<<5;
	return seed;
}

const int maxn=20000100;
int prime[maxn],cnt=0,n;
bool ha[maxn];
uint a[maxn];

void Prime(void)
{
    ha[1]=true;
    for(int i=2;i<=n;i++)
    {
        if(!ha[i]) prime[++cnt]=i;
        for(int j=1;j<=cnt&&prime[j]*i<=n;j++)
        {
            ha[prime[j]*i]=true;
            if(i%prime[j]==0) break;
        }
    }
}

int main(void)
{
    scanf("%d%u",&n,&seed);
    Prime();
    for(int i=1;i<=n;i++)
        a[i]=getnext();
    for(int i=1;i<=cnt;i++)
        for(int j=1;j*prime[i]<=n;j++)
            a[j*prime[i]]+=a[j];
    uint ans=0;
    for(int i=1;i<=n;i++)
        ans^=a[i];
    printf("%u\n",ans);
    return 0;
}