A 1-interesting polygon is just a square with a side of length 1. An n-interesting polygon is obtained by taking the n - 1-interesting polygon and appending 1-interesting polygons to its rim, side by side. You can see the 1-, 2-, 3- and 4-interesting polygons in the picture below.

Example

• For n = 2, the output should be
  shapeArea(n) = 5;
• For n = 3, the output should be
  shapeArea(n) = 13.

我的解答：

def shapeArea(n):

    return 2*n*n - 2*n + 1

膜拜大佬：

def shapeArea(n):

    return n**2 + (n-1)**2