CF230B T-primes 我们知道质数是只有两个不同的正数因数的正整数.相似的,我们把一个正整数 t 叫做 T质数,如果 t 恰好有三个不同的正整数因数. 你被给了一个含有 n 个正整数的数组.你要给其中所有的数判断它是否是 T质数. 可以知道一个质数的完全平方数有且只有三个因子. 然后这题就水了. 线性筛出1到$\sqrt{a_i} $的素数,判断就行了. code: #include <iostream> #include <cstdio> #include <cm…

Summation of Four Primes Input: standard input Output: standard output Time Limit: 4 seconds Euler proved in one of his classic theorems that prime numbers are infinite in number. But can every number be expressed as a summation of four positive prim…

题意:统计小于n的质数个数. 作为一个无节操的楼主,表示用了素数筛法,并没有用线性素数筛法. 是的,素数筛法并不是该题最佳的解法,线性素数筛法才是. 至于什么是素数筛法,请百度吧. class Solution { public: int countPrimes(int n) { bool *isp= new bool[n]; ; i < n; ++i) { isp[i]= true; } ; i * i< n; ++i)//素数筛法 { if(isp[i]){ for(int j = i +…

Arithmancy is Draco Malfoy's favorite subject, but what spoils it for him is that Hermione Granger is in his class, and she is better than him at it. Prime numbers are of mystical importance in Arithmancy, and Lucky Numbers even more so. Lucky Number…

Lucas的数论 reference 题目在这里> < Pre 数论分块 默认向下取整时. 形如\(\sum\limits_{i=1}^n f\left( \frac{n}{i}\right)\)的求和,由于\(\frac{n}{r}\)的值只有\(\sqrt{n}\)个,可以直接数论分块上. 题解 记原式为\(S(n)\),有 \[S(n)=\sum_{i\rightarrow n}\sum_{j\rightarrow n}[\gcd{i,j}=1]\frac{n}{i}\frac{n}{j…

Problem Description Writea program to read in a list of integers and determine whether or not eachnumber is prime. A number, n, is prime if its only divisors are 1 and n. Forthis problem, the numbers 1 and 2 are not considered primes. Input Eachinput…

上期为大家介绍了目前常见加密算法,相信阅读过的同学们对目前的加密算法也算是有了一个大概的了解.如果你对这些解密算法概念及特点还不是很清晰的话,昌昌非常推荐大家可以看看HTTPS的加密通信原理,因为HTTPS加密通信使用了目前主要的三种加密算法,大家可以从中体会到各种加密算法的优缺点. 一.目前常见加密算法简介 二.RSA算法介绍及数论知识介绍 三.RSA加解密过程及公式论证 二.RSA算法介绍及数论知识介绍 如果上期(目前常见加密算法简介)算是天安门前的话,那今天的内容就算是正式通过天安门进入故…

Special Prime Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 738    Accepted Submission(s): 390 Problem Description Give you a prime number p, if you could find some natural number (0 is not in…

题目链接 https://www.51nod.com/Challenge/Problem.html#!#problemId=1238 题解 本来想做个杜教筛板子题结果用另一种方法过了...... 所谓的"另一种方法"用到的一些技巧还是挺不错的,因此这里简单介绍一下. 首先还是基本的推式子: \[\begin{aligned}\sum_{i = 1}^n \sum_{j = 1}^n {\rm lcm}(i, j) &= \sum_{i = 1}^n \sum_{j = 1}^n…

Problem Description Let f(x) = anxn +...+ a1x +a0, in which ai (0 <= i <= n) are all known integers. We call f(x) 0 (mod m) congruence equation. If m is a composite, we can factor m into powers of primes and solve every such single equation after wh…