Maths

Problem Given an integer n, return true if n is a perfect number, otherwise return false. Definition A perfect number is a natural number that is equal to the sum of its positive divisors, excluding the number itself. A divisor of an integer x is an integer that can divide x evenly. The first perfect numbers are 6, 28, 496, 8128 and all of them are in form $$ 2^{n-1}.(2^n - 1)$$ ...

Problem There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner. ...