The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.</p>
There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.</p>
How many circular primes are there below one million?</p> </div>
|
Answer:</div></td>
55</b></td></tr></tbody></table>#include | #include #include #define MAX 1e6 int isprime(long n) { int i=3; if(n==2||n==3||n==5||n==7)return 1; if(n%2==0)return 0; for(i=3;i*i<=n;i+=2) if(n%i==0)return 0; return 1; } int dig(long i) { int n=0; while(i) { i/=10; n++; } return n; } int *rotations(long i,int m) { int j=0,carry,tmp; int *p=(int*)malloc((m-1)*sizeof(long)); tmp=i; for(j=0;j carry=pow(10,m-1); p[j]=tmp%carry*10+tmp/carry; tmp=p[j]; } return p; } int main (int argc, char const* argv[]) { int j,flag=1,i=0,k; long n,sum; int *tmp=NULL; for(n=2;n j=dig(n); tmp=rotations(n,j); for(k=0,flag=1;k flag=0; if(flag&&isprime(n)) i++; } printf("%dn",i); return 0; } </div> 分析预测模型在机器学习中的应用之线性回归回归能做任何事情 Continue reading android中的线程与进程模型Published on June 15, 2016android内存优化之图片加载Published on June 11, 2016 |