When you create a product there is the option to set the minimun and maximun quantity of products in the cart. It’s in the inventory tab. You could put the min and max setting to 10 (for example) so the customer it’s obligated to add 10. But I don’t know if it will tell the customer the X number of articles needed or just throws an error.
You could create a product which already has an X number of products in it.
Instead of Pen x1, just put Pen x12 and put the price of the article to be twelve times that.
Does it help?