# Task
 Below we will define what and n-interesting polygon is and your task is to find its area for a given n.

 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- and 3-interesting polygons in the picture below.

 ![](https://files.gitter.im/myjinxin2015/Gwsw/blob)

# Example

 For `n = 1`, the output should be `1`;
 
 For `n = 2`, the output should be `5`;
 
 For `n = 3`, the output should be `13`.

# Input/Output


 - `[input]` integer `n`

    Constraints: `1 ≤ n < 10000.`
    

 - `[output]` an integer

   The area of the n-interesting polygon.

Difficulty: introductory

Starter code:

def shape_area(n):
	

Solutions:
def shape_area(n):
    return n**2 + (n - 1) ** 2

def shape_area(n):
    return 2 * n * (n - 1) + 1

def shape_area(n):
    if n==1:
        return 1
    return n*n*2-n-(n-1)

def shape_area(n):
  p = 0
  area = 1
  for i in range (1, n):
      p = n*4-4
      n -= 1
      area += p
  return area
  


tr = lambda n: (n*(n+1))//2 if n>=0 else 0
shape_area = lambda n: tr(n)+2*tr(n-1)+tr(n-2)

#https://en.wikipedia.org/wiki/Centered_square_number

def shape_area(n):
  return n**2 + (n-1)**2

def shape_area(n):
  return sum([4*(e-1) for e in range(n,1,-1)])+1

def shape_area(n):
    res=1
    for x in range(1,n):
        res += x*4
        
    return res

def shape_area(n):
  return 2*n*n - 2*n + 1

def shape_area(n):
  #1 1
  #2 5 1 + 3 + 1
  #3 13 1 + 3 + 5 + 3 + 1
  #4 25 1 + 3 + 5 + 7 + 5 + 3 + 1
    return 2 * sum(x for x in range(1, 2*(n-1), 2)) + (2*n - 1)