(Problem 37)Truncatable primes
The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3.
Find the sum of the only eleven primes that are both truncatable from left to right and right to left.
NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes.
题目大意:
3797这个数很有趣。它本身是质数,而且如果我们从左边不断地裁去数字,得到的仍然都是质数:3797,797,97,7。而且我们还可以从右向左裁剪:3797,379,37,3,得到的仍然都是质数。
找出全部11个这样从左向右和从右向左都可以裁剪的质数。
注意:2,3,5和7不被认为是可裁剪的质数。
//(Problem 37)Truncatable primes
// Completed on Thu, 31 Oct 2013, 13:12
// Language: C
//
// 版权所有(C)acutus (mail: acutus@126.com)
// 博客地址:http://www.cnblogs.com/acutus/
#include<stdio.h>
#include<math.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#include<stdbool.h> bool isprim(int n)
{
int i=;
if(n==) return false;
for(; i*i<=n; i++)
{
if(n%i==) return false;
}
return true;
} bool truncatable_prime(int n)
{
int i,j,t,flag=;
char s[];
int sum=;
sprintf(s,"%d",n);
int len=strlen(s); if(!isprim(s[]-'') || !isprim(s[len-]-'')) return false; for(i=; i<len-; i++)
{
t=s[i]-'';
if(t== || t== || t== || t== || t== || t==) return false;
} for(i=; i<len-; i++)
{
for(j=i; j<len-; j++)
{
sum+=s[j]-'';
sum*=;
}
sum+=s[j]-'';
if(!isprim(sum)) return false;
sum=;
}
j=len-;
i=;
while(j>i)
{
for(i=; i<j; i++)
{
sum+=s[i]-'';
sum*=;
}
sum+=s[i]-'';
if(!isprim(sum)) return false;
sum=;
i=;
j--;
}
return true;
} int main()
{
int sum,count;
sum=count=;
int i=;
while()
{
if(isprim(i) && truncatable_prime(i))
{
count++;
sum+=i;
//printf("%d\n",i);
}
i=i+;
if(count==) break;
}
printf("%d\n",sum);
return ;
}
Answer:
|
748317 |
(Problem 37)Truncatable primes的更多相关文章
- (Problem 35)Circular primes
The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, ...
- (Problem 47)Distinct primes factors
The first two consecutive numbers to have two distinct prime factors are: 14 = 2 7 15 = 3 5 The fi ...
- (Problem 49)Prime permutations
The arithmetic sequence, 1487, 4817, 8147, in which each of the terms increases by 3330, is unusual ...
- (Problem 73)Counting fractions in a range
Consider the fraction, n/d, where n and d are positive integers. If nd and HCF(n,d)=1, it is called ...
- (Problem 42)Coded triangle numbers
The nth term of the sequence of triangle numbers is given by, tn = ½n(n+1); so the first ten triangl ...
- (Problem 41)Pandigital prime
We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly o ...
- (Problem 70)Totient permutation
Euler's Totient function, φ(n) [sometimes called the phi function], is used to determine the number ...
- (Problem 74)Digit factorial chains
The number 145 is well known for the property that the sum of the factorial of its digits is equal t ...
- (Problem 46)Goldbach's other conjecture
It was proposed by Christian Goldbach that every odd composite number can be written as the sum of a ...
随机推荐
- openstack windows 2008 img
1,制作镜像主机pre Env yum -y install qemu-img virt-install libvirt 2,配置bridge
- Hive索引
1. Hive索引概述 Hive的索引目的是提高Hive表指定列的查询速度. 没有索引时.类似'WHERE tab1.col1 = 10' 的查询.Hive会载入整张表或分区.然后处理全 ...
- Android Animation学习(二) ApiDemos解析:基本Animatiors使用
Animator类提供了创建动画的基本结构,但是一般使用的是它的子类: ValueAnimator.ObjectAnimator.AnimatorSet ApiDemos中Animation部分是单独 ...
- Nice way for strip_tags a like
I found this code works great as the function strip_tags in php to replace html tags from string and ...
- iOS 自定义各类bar的属性
在iOS应用开发中,经常需要为导航栏和标签栏设置相同的主题,一个一个去设置的话,就太麻烦了,可以通过对应用中所有的导航栏和标签栏同意设置背景.字体等属性. 如:创建一个继承自“UINavigation ...
- (转)原子操作 Interlocked系列函数
上一篇<多线程第一次亲密接触 CreateThread与_beginthreadex本质区别>中讲到一个多线程报数功能.为了描述方便和代码简洁起见,我们可以只输出最后的报数结果来观察程序是 ...
- C/C++中字符串的输入问题
standard C I/O 头文件:#include <stdio.h> . getchar() 原型:int getchar(void); 功能:从标准输入获取并返回下一个字符,并释放 ...
- 基于MAVEN的SSM+ehcache+c3p0
目录结构: 2.pom.xml <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http ...
- ASP.NET jQuery 随笔 使用jQuery UI的Autocomplete方法实现文本框的自动搜索填充功能
首先当然是去下载JQuery UI ,这里这里是下载地址http://jqueryui.com/ 第一步是点击这里 第二步选择你想要下载的主题进行下载 我这里是选择的cupertino主题包 点击圆圈 ...
- Spring Boot普通类调用bean
1 在Spring Boot可以扫描的包下 假设我们编写的工具类为SpringUtil. 如果我们编写的SpringUtil在Spring Boot可以扫描的包下或者使用@ComponentScan引 ...