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Description
Sigma function is an interesting function in Number Theory. It is denoted by the Greek letter Sigma (σ). This function actually denotes the sum of all divisors of a number. For example σ(24) = 1+2+3+4+6+8+12+24=60. Sigma of small numbers is easy to find but for large numbers it is very difficult to find in a straight forward way. But mathematicians have discovered a formula to find sigma. If the prime power decomposition of an integer isThen we can write,
For some n the value of σ(n) is odd and for others it is even. Given a value n, you will have to find how many integers from 1 to n have even value of σ.
Input
Input starts with an integer T (≤ 100), denoting the number of test cases.Each case starts with a line containing an integer n (1 ≤ n ≤ 1012).
Output
For each case, print the case number and the result.Sample Input
4 3 10 100 1000 Sample Output Case 1: 1 Case 2: 5 Case 3: 83 Case 4: 947嘛,我是找不到这规律,真是咸鱼。。。
以下是别人的解题思路 解题思路: 开始就根据公式,发现只要乘积中出现一个偶数即可。然后各种打表算啊。。。 结果发现N=10000的时候程序出结果都很慢。。。这样交上去肯定TLE。 然后打表,打出100之内所有符合条件的数,然后找规律。。。。 发现只要是2^x,x^2,2*x^2…只有这种数没有出现过。所以,我们直接去重即可。 但是这些直接去重我们会发现减去的这些值有重复的,所以我们要判断下。 ①2^x和x^2, 当x为偶数时二者出现重复。 ②2^x和2*x^2,当x为奇数时,二者出现重复。 所以直接用N值减去x^2和2*x^2的值就是我们要的结果。#include#include #include #include #include #include #include
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