题解：筛出约数，然后计算即可。
#include <cstdio>
#include <algorithm>
typedef long long LL;
LL a1[1000005],a2[1000005],x,y,k,g;
int cnt1,cnt2,T;
LL gcd(LL a,LL b){if(b==0)return a;else return gcd(b,a%b);}
int main(){
scanf("%d",&T);
while(T--){
scanf("%I64d%I64d%I64d",&x,&y,&k);
g=gcd(x,y); cnt1=cnt2=0;
if(k==1){printf("%I64d\n",g);continue;}
if(k>2000010){puts("-1");continue;}
for(LL i=1;i*i<=g;i++)if(g%i==0){
a1[++cnt1]=i;
if(i*i!=g)a2[++cnt2]=g/i;
}if(k>cnt1+cnt2)puts("-1");else if(k<=cnt2)printf("%I64d\n",a2[k]);else printf("%I64d\n",a1[cnt1-k+cnt2+1]);
}return 0;
}
//注意循环也要用long long 否则会出错