Simpler data structure?

* 846af413 [sieve.py #L29](https://github.com/kangwonlee/sieve/blob/846af413b0f9e13d19ecbadcd186885732ea56d9/sieve.py#L29)
* Currently using `ttk.Treeview`
* A possibly more desirable example [link](https://github.com/kangwonlee/sieve/blob/91e15738714fdd39b1761331a4754059efa499f9/sieve_oop.ipynb)
``` python
class Sieve_ipynb:
def __init__(self, n, col=10):
self.n = n
self.col = col
self.row = n // col

self.table = np.array(range(n))

self.table[0] = 0
self.table[1] = 0

```

Start at sieve.py line 29, where the current ttk.Treeview is referenced, then compare it with the Sieve_ipynb example in sieve_oop.ipynb. Determine whether the notebook's table representation is intended to replace the current structure; done should mean the simpler representation works for the existing sieve display.

Written by the indexing model from the issue text.