大意

求$gcd(a,b)=a\ xor\ b$gcd(a,b)=a xor b，$a,b\in[1..n]$a,b∈[1..n]的方案数

思路

手推思路见个人思考过程
题解:

代码

#include<cstdio>
using namespace std;int n,a,b,ans;
inline int gcd(register int x,register int y){return y?gcd(y,x%y):x;}
signed main()
{
	scanf("%d",&n);
	for(register int c=1;c<=n/2;c++)
	 for(register int a=c*2;a<=n;a+=c)
	if((a-c)==(a^c)) ans++;
	printf("%d",ans);
}