a(1) = 23:
._______. ._______. ._______. ._______. ._______. ._______.
| .___| | |_______| | |___. | |_______| | | | | | ._|_. |
|_|_____| | .___| | |_____|_| | |___. | | |___| | | | | |
|_______| |_|_____| |_______| |_____|_| |___|___| |_|___|_|
._______. ._______. ._______. ._______. ._______. ._______.
| ._| | | | .___| | |_. | |___. | | | | | |_______|
| | |___| | |_| | |___| | | | |_| | |___|___| | | |
|_|_____| |___|___| |_____|_| |___|___| |_______| |___|___|
._______. ._______. ._______. ._______. ._______. ._______.
| ._| ._| | |___. | |_. |_. | | .___| | | ._| | | | | |_. |
| |___| | | |_. |_| | |___| | |_| ._| | | | _| | | |_. | |
|_|_____| |___|___| |_____|_| |___|___| |_|_|___| |___|_|_|
._______. ._______. ._______. ._______. ._______.
|_. ._| | | |_. ._| | .___| | | |___. | |_______|
| |_|_. | | ._|_| | |_| |_. | | ._| |_| |_______|
|_____|_| |_|_____| |_____|_| |_|_____| |_______|.
|