# LeetCode-math类总结(会持续更新...)

## 204. Count Primes

Description:

Count the number of prime numbers less than a non-negative number, n.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

## 263. Ugly Number

Description:Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include `2, 3, 5`. For example, `6, 8` are ugly while `14` is not ugly since it includes another prime factor `7`.

Note that `1` is typically treated as an ugly number.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

## 400. Nth Digit

Description:Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, …

Note:
n is positive and will fit within the range of a 32-bit signed integer (n < 231).

Example 1:

Example 2:

## 633. Sum of Square Numbers

Description:Given a non-negative integer `c`, your task is to decide whether there’re two integers `a` and `b` such that a2 + b2 = c.

Example 1:

Example 2:

## 367. Valid Perfect Square

Description:

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Note: Do not use any built-in library function such as `sqrt`.

Example 1:

Example 2:

Credits:
Special thanks to @elmirap for adding this problem and creating all test cases.

## 172. Factorial Trailing Zeroes

Description:

Given an integer n, return the number of trailing zeroes in n!.

**Note: **Your solution should be in logarithmic time complexity.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.