#--- iterative
def f1(n):
    s = 0
    for i in range(1,n,2):
        s = s + i**2
    return(s)

#--- recursive

import turtle
def f2(t, d, n):
    if n==0:
        t.forward(d)
    else:
        f2(t, 0.45*d, n-1)
        t.left(90)
        f2(t, 0.45*d, n-1)
        t.right(90)
        t.forward(0.10*d)
        t.right(90)
        f2(t, 0.45*d, n-1)
        t.left(90)
        f2(t, 0.45*d, n-1)
    return()

alice = turtle.Turtle()
alice.up()
alice.goto(-300,0)
alice.down()
f2(alice, 400, 3)