https://codeforces.com/problemset/problem/1542/C
题意:
定义\(f(i)\)表示最小的不能整除i的数,求\(\sum_{i=1}^nf(i)\)
若\(f(i)=x\),说明\(1|i,2|i,3|i,……(x-1)|i,x \nmid i\),即\(lcm(1,2,3,……,x-1) | i,x \nmid i\)
所以\(f(i)>=x\)的\(i\)的个数等于 \(n/lcm(1,2,3,……,x-1)\)
\(f(i)=x\)的\(i\)的个数等于 \(n/lcm(1,2,3,……,x-1)\) - \(n/lcm(1,2,3,……,x-1,x)\)
#include<bits/stdc++.h> using namespace std; long long getgcd(long long a,long long b) { return __gcd(a,b); } long long getlcm(long long a,long long b) { return a/getgcd(a,b)*b; } int main() { int T; long long n,lcm; const int mod=1e9+7; int ans; scanf("%d",&T); while(T--) { scanf("%lld",&n); ans=0; lcm=1; for(int i=1;;++i) { lcm=getlcm(i,lcm); if(lcm>n) break; ans+=n/lcm%mod; ans%=mod; } ans=(ans+n)%mod; printf("%d\n",ans); } }