# 2579. Count Total Number of Colored Cells
###### tags: `Leetcode` `Medium` `Math`
Link: https://leetcode.com/problems/count-total-number-of-colored-cells/description/
## 思路
找规律
每个图案的colored cells个数是1+3+...+2n-1+2n-3+...+3+1
也就是两个等差数列求和

1+3+...+2n-1 = n*n
2n-3+...+3+1 = (n-1)*(n-1)

## Code

class Solution:
    def coloredCells(self, n: int) -> int:
        return n*n+(n-1)*(n-1)