divisors pairs

void foo (int n){
    vector <int>largest_divisor(n,0);
    vector <int> n_divisor(n,0);//number of divisors
    largest_divisor[1]=1;
    for (int i=2; i<n; i++){ //sieve
        if (largest_divisor[i]==0){
            for (int j=i; j<n; j+=i )
                largest_divisor[j]=i;
        }
    }

    n_divisor[1]=1;
    for (int i=2; i<n; i++){
        int p=largest_divisor[i];
        int pk=1; // p^k in k-th inner iteration
        int div=1; //number of divisors of p^k
        int m=i;
        do{
            pk*=p;
            div+=pk;
            m/=p;
        }while (m%p==0);
        n_divisor[i] = div * n_divisor[m];
    }

    auto f = [&](int x) { return n_divisor[x]-x -1; }; //number of proper divisors-1

    //look for solutions
    for (int i=2; i<n; i++){
        if ( f(i)<=i ){
            if  (f(f(i))==i){
                cout << i << " "<<f(i) <<endl;
            }
        }
    }

}


/* results < 100'000'000
75 48
195 140
1648 1575
1925 1050
2295 2024
6128 5775
16587 8892
20735 9504
75495 62744
206504 186615
219975 196664
309135 199760
507759 266000
544784 526575
549219 312620
817479 573560
1057595 587460
1159095 1139144
1331967 1081184
1341495 1173704
1348935 1208504
1459143 1236536
1524831 1233056
1763019 1140020
1902215 1000824
2142945 2102750
2226014 1921185
2421704 2140215
2576945 1279950
2681019 2036420
3010215 2312024
3123735 2198504
3220119 2171240
3676491 2958500
4282215 4012184
5644415 2580864
6446325 5088650
7509159 5416280
7890575 4311024
9345903 6081680
10106504 9247095
10925915 7460004
12251679 6618080
12900734 12500865
13693959 8713880
16247745 12146750
16381925 7875450
18845855 8829792
26502315 22559060
26525415 23379224
27862695 27735704
28206815 14371104
31213899 13922100
31356314 23939685
32014575 28219664
37291625 22013334
41950359 26409320
42125144 40818855
43321095 34093304
52389315 49217084
58354119 33299000
69090615 66086504
70112175 64045904
80870615 37324584
84854315 41137620
85141719 52026920
87689415 66275384
87802407 76011992
88567059 61423340
93423519 62252000
96751395 94970204
97389039 52601360
99735705 93993830
*/