Code.cpp

VL sieve(ll n) {
    ll  check[n+5];
    VL primes ;
    memset(check,0,sizeof(check));
    check[1] = 1 ;
    for ( ll i = 4 ; i <= n ; i = i+2) check[i] = 1 ;  

    for ( ll i = 3 ; i*i <= n ; i += 2) {                
        if (!check[i]) {                                
            for ( ll j = i*i ; j <= n ; j += 2*i){       
                   check[j] = 1 ;                        
            }                                            
        }                                                
    }   

    for ( ll i = 1 ; i <= n ; i++)  if (!check[i]) primes.PB(i);   
    return primes ;
}

ll sumofdivisors(ll n) {
    ll primerange = (ll)sqrt(n)+1 ;
    VL primes = sieve(primerange);
    if ( n == 1) return 1 ;
    ll sod = 1 ;
    for ( ll i = 0 ;  primes[i] <= sqrt(n) && i < primes.size() ; i++) {
        if ( n%primes[i] == 0 && primes[i] <= n) {
            ll cnt = 0 ;
            ll val = 1 ;
            while (!(n%primes[i])) {
                n = n/primes[i];
                cnt = cnt+val ;
                val = val*primes[i];
            }
            sod = sod*(cnt+val); 
        }
    }
    if ( n > 1) sod = sod*(n+1);
    return sod ;
}