题面
首先题目给的柿子实际上就是$n$的因子个数
$[l,r]$运用前缀和拆成$[1,r]-[1,l-1]$
数论分块
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using namespace std;
typedef long long ll;
const ll mod = 998244353;
inline int (ll x) {
int ans = 0;
for(ll l = 1, r; l <= x; l = r + 1) {
r = x / (x / l);
ans = (ans + 1ll * (r - l + 1) * (x / l)) % mod;
}
return ans;
}
int main() {
ll l, r;
scanf("%lld%lld", &l, &r);
return printf("%lldn", (work(r) - work(l - 1) + mod) % mod), 0;
}
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