a(1)=9:
.___. .___. .___. .___. .___. .___. .___. .___. .___.
| | | | | | | |_. | | | | ._| | | | ._| |_. |
|___| | | | |___| | | | |___| | | | |___| | | | | | |
| | | | | | | | | |_| |_. | |_| | | ._| |_| | | |_|
|___| |_|_| | | | |___| | | | |___| | | | | | | | | |
| | | | | | | | | | |_| | | |_| | | |_| |_| |
|___| |___| |_|_| |___| |___| |___| |___| |___| |___|.
|