Project Euler 28

def diagonals(n):
    sumOfDiag = 1
    lastDiag = 1
    for length in range(3, n + 1, 2):
        for x in range(0, 4, 1):
            corner = lastDiag + length - 1
            sumOfDiag += corner
            lastDiag = corner
    return sumOfDiag

diagonals(1001)