玲珑学院-1010-Alarm【打表】【找规律】【思维】

题目链接：点击打开链接

1010- Alarm

Time Limit：1s Memory Limit：128MByte

Submissions：236Solved：82

DESCRIPTION

Given a number sequence $[3,7,22,45,116,...]$. Please tell me the $k$-th number.

INPUT

A number $T(T<100)$ indicates the number of the input cases. Then for each case there only is one integer $k(1\le k\le 10000)$.

OUTPUT

For each case, ouput the $k$-th number of the sequence in one line.

SAMPLE INPUT

214

SAMPLE OUTPUT

345

题解：规律就是第 n 个素数的平方减去n：2 ^ 2 - 1，3 ^ 2 - 2，5 ^ 2 - 3，7 ^ 2 - 4，11 ^ 2 - 5 ............

贴个水水的代码：

#include<cstdio>#include<algorithm>using namespace std;const int MAX=1e7;typedef long long LL;bool sushu[MAX+10]={1,1};LL a[MAX+10];void init(){for(LL i=1;i<=MAX;i++){if(sushu[i]==1)continue;for(LL j=i*2;j<=MAX;j=j+i){sushu[j]=1;}}LL k=1;for(LL i=2;i<=MAX;i++){if(sushu[i]==0){a[k++]=i;}}}int main(){int t;scanf("%d",&t);init();while(t--){int n;scanf("%d",&n);printf("%lld\n",a[n]*a[n]-n);}return 0;}