In this particular case the set $A_i$ - previously mentioned in the tutorial section - denotes how many qudruples $\{ V_1, V_2, V_3, V_4\}$ there are such that $i \mid V_j, \forall i \in [1,4]$. The global answer is $\bigg| \bigcup_{i=1}^{\text{ maxval }} A_i \bigg|$.

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#include <iostream>
#include <vector>

using namespace std;

void precompute(vector<int> &mobius, vector<int> &comb) {
	mobius[1] = -1;
	for (int i = 1; i < (int)mobius.size(); i++) {
		if (mobius[i]) {
			mobius[i] = -mobius[i];