Topic and post numbers / Notification of posts

I would like to have a number assigned to each new topic, and to each post within the topic.

This would make it much easier for users to refer to a previoius post. We could say:
"Re: Topic x, Post y".

Topic numbers would be reset to 1 on January 1 every two years.

It would also be helpful to have some way of being notified by email about new posts. We should be able to choose between individual notifications, daily notifications and weekly notifications of new posts on a particular topic.